Wireless Communications

A cellular base station serves a multiplicity of single-antenna terminals over the same time-frequency interval. Time-division duplex operation combined with reverse-link pilots enables the base station to estimate the reciprocal forward- and reverse-link channels. The conjugate-transpose of the channel estimates are used as a linear precoder and combiner respectively on the forward and reverse links. Propagation, unknown to both terminals and base station, comprises fast fading, log-normal shadow fading, and geometric attenuation. In the limit of an infinite number of antennas a complete multi-cellular analysis, which accounts for inter-cellular interference and the overhead and errors associated with channel-state information, yields a number of mathematically exact conclusions and points to a desirable direction towards which cellular wireless could evolve. In particular the effects of uncorrelated noise and fast fading vanish, throughput and the number of terminals are independent of the size of the cells, spectral efficiency is independent of bandwidth, and the required transmitted energy per bit vanishes. The only remaining impairment is inter-cellular interference caused by re-use of the pilot sequences in other cells (pilot contamination) which does not vanish with unlimited number of antennas.

Noncooperative Cellular Wireless with Unlimited Numbers of Base Station Antennas

Multiple-input multiple-output (MIMO) technology is maturing and is being incorporated into emerging wireless broadband standards like long-term evolution (LTE) [1]. For example, the LTE standard allows for up to eight antenna ports at the base station. Basically, the more antennas the transmitter/receiver is equipped with, and the more degrees of freedom that the propagation channel can provide, the better the performance in terms of data rate or link reliability. More precisely, on a quasi static channel where a code word spans across only one time and frequency coherence interval, the reliability of a point-to-point MIMO link scales according to Prob(link outage) ` SNR-ntnr where nt and nr are the numbers of transmit and receive antennas, respectively, and signal-to-noise ratio is denoted by SNR. On a channel that varies rapidly as a function of time and frequency, and where circumstances permit coding across many channel coherence intervals, the achievable rate scales as min(nt, nr) log(1 + SNR). The gains in multiuser systems are even more impressive, because such systems offer the possibility to transmit simultaneously to several users and the flexibility to select what users to schedule for reception at any given point in time [2].

/pdf/scaling-up-mimo-opportunities-and-challenges-with-very-large-puqp9v7gzk.pdf

Scaling Up MIMO: Opportunities and Challenges with Very Large Arrays

The quintessential goal of sensor array signal processing is the estimation of parameters by fusing temporal and spatial information, captured via sampling a wavefield with a set of judiciously placed antenna sensors. The wavefield is assumed to be generated by a finite number of emitters, and contains information about signal parameters characterizing the emitters. A review of the area of array processing is given. The focus is on parameter estimation methods, and many relevant problems are only briefly mentioned. We emphasize the relatively more recent subspace-based methods in relation to beamforming. The article consists of background material and of the basic problem formulation. Then we introduce spectral-based algorithmic solutions to the signal parameter estimation problem. We contrast these suboptimal solutions to parametric methods. Techniques derived from maximum likelihood principles as well as geometric arguments are covered. Later, a number of more specialized research topics are briefly reviewed. Then, we look at a number of real-world problems for which sensor array processing methods have been applied. We also include an example with real experimental data involving closely spaced emitters and highly correlated signals, as well as a manufacturing application example.

Two decades of array signal processing research: the parametric approach

It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

On the capacity of a cellular CDMA system

First network node 110 and method in the first network node 110 for configuring a second network node 120 to operate either in cell mode or in beam mode when communicating with a user equipment 130, 140. The method comprises obtaining information for determining the operative mode of the second network node 120, comparing the obtained information with a threshold value, determining the operative mode of the second network node 120, based on the made comparison, and configuring the second network node 120 in cell mode or in beam mode, in relation to the user equipment 130,140, according to the determined operative mode of the second network node 120. A user equipment 130, 140 and a method in a user equipment 130, 140 is also disclosed.

Methods and nodes in a wireless communication network

A communication unit (10, 20, 40) and a method for communicating at least one signal over a channel of a first channel type and at least one signal over a channel of a second channel type, which is different from the first channel type. The apparatus comprises a timer (19, 30, 50) adapted to schedule a predetermined time period, during which interference due to simultaneous communication of signals over the channel of the first channel type and the channel of the second channel type is anticipated. Also, the apparatus comprises a processing unit (16, 29, 49) adapted to apply, during the predetermined time period, an interference counteracting process for counteracting interference between any signal communicated over the channel of the first channel type and any signal communicated over the channel of the second channel type. The interference counteracting process comprises changing, during the predetermined time period, from a first to a second format for representing information transmitted over the channel of the first channel type, the second format being more robust than the first format.

Method and device for communicating a signal

The invention is based on the recognition that conventional pilot-based channel quality estimation does not take into account the future transmission activity of neighboring access points, and that this may lead to inaccurate channel quality estimation as well as inefficient link adaptation. By controlling the transmission power of the pilots based on future data transmission activity, the transmission conditions during the pilot-based estimation of channel quality (e.g. frame n) can be correlated to the transmission conditions of the future frame (e.g. frame n+1) in which the corresponding modulation and coding scheme is to be used. In this way, more accurate predictions of the channel quality can be made so that optimal or near-optimal modulation and coding schemes can be selected during link adaptation. This in turn results in increased link data rates.

Link adaptation method and quality estimation in a cellular radio system

An asynchronous direct-sequence code division multiple access (DS-CDMA) communication system operating over an additive white Gaussian noise (AWGN) channel is considered. In many applications, the near-far problem can be the limiting factor. Several near-far resistant receivers have therefore been proposed (e.g., the decorrelating receiver). These receivers assume perfect knowledge of the propagation delay from all users to the receiver. In practice, the delays are estimated and therefore subject to estimation errors. The performance penalty these errors impose on linear detectors, especially the decorrelating detector, is evaluated.

Sensitivity analysis of linear DS-CDMA detectors to propagation delay estimation errors

This chapter covers the background to, and basic principles for 5G wireless access. It describes the key requirements for 5G wireless access, including the requirements of IMT-2020 as defined by ITU. It goes on to discuss the 5G spectrum situation and the overall structure of 5G wireless access consisting of the evolution of LTE in combination with a new radio-access technology. Finally, it gives an overview of the 3GPP process with regard to 5G, including the time schedule developed to ensure timely 5G commercial introduction in 2020.

Stefan Parkvall

Papers

Methods and nodes in a wireless communication network

Method and device for communicating a signal

Link adaptation method and quality estimation in a cellular radio system

Sensitivity analysis of linear DS-CDMA detectors to propagation delay estimation errors

5G Wireless Access