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].

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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

FIELD: information technologies. ^ SUBSTANCE: cellular communication system, which applies orthogonal frequency division in its radio interface, may use either the first diversion of subcarriers or the second diversion of subcarriers. The one used at the moment is indicated by generation of the first type of a sync signal, in response to the first diversion of subcarriers used at this moment, and generation of the second type of a sync signal in response to the second diversion of subcarriers used at the moment. Any of the generated first type of the sync signal and the second type of the sync signal is transmitted. To differentiate between the first and second types of sync signals, provision of the time area of the second type of the sync signal includes multiple copies of the first type of the sync signal. ^ EFFECT: reduced time of cell searching. ^ 22 cl, 10 dwg

Identification of subcarrier diversion

Underlay network node and macro base station and methods therein for enabling avoidance of interference in a cell extension area associated with an uplink/downlink imbalance. The underlay network node is assumed to be associated with a cell area A, and a cell extension area B, where the cell extension area B has an uplink/downlink imbalance in relation to a neighboring base station and the network node. The method in the underlay network node involves serving a UE in both uplink and downlink when the UE is located in cell area A. The method further involves serving a UE only in the uplink when the UE is located in cell extension area B, thus enabling avoidance of interference related to communication of a UE located in said cell extension area B.

Method and arrangement for relaying in case of extension areas having uplink/downlink imbalance

The present invention generally relates to radio communication systems, relay nodes, controller nodes, user equipment (user terminals), software and methods for said systems and nodes. In one embodiment, a method for operating a control node for a wireless communication system is provided. The method comprises the steps: creating a data frame comprising an early part and a later part, wherein the early part comprises first control data for controlling a receiving node; checking whether second control data are to be put into the later part; scheduling payload data for the receiving node into the later part if second control data are not to be put into the later part; and transmitting the data frame to the receiving node.

Methods and nodes in a radio communication system

in this paper, several receivers for data demodulation in an asynchronous direct-sequence code-division multiple access (DS-CDMA) system operating without prior knowledge of the propagation delays are proposed and compared. Special attention is paid to the near-far problem, and the proposed schemes are numerically shown to be near-far robust. The near-far robustness is obtained by estimating the a priori unknown propagation delay using a subspace-based technique. Quantities obtained in the estimation procedure are subsequently used to design an interference suppression filter according to the minimum mean-squared error criterion. A simple two-state Viterbi algorithm is used for the data demodulation in the uncoded case. By extending the trellis used in the Viterbi algorithm, error correcting coding is easily implemented.

Coded asynchronous near-far resistant DS-CDMA receivers operating without synchronization

In this paper we consider the problem of estimating the propagation delays and relative amplitudes of the transmitted signals as well as detecting the data bits in an asynchronous direct-sequence code division multiple access (DS-CDMA) system operating over a fading channel. A subspace based estimator is proposed for estimating the propagation delays. The path gains and data bits are estimated with minimum mean squared error techniques. Special attention is paid to the near-far problem.

Stefan Parkvall

Papers

Identification of subcarrier diversion

Method and arrangement for relaying in case of extension areas having uplink/downlink imbalance

Methods and nodes in a radio communication system

Coded asynchronous near-far resistant DS-CDMA receivers operating without synchronization

Parameter Estimation and Detection of DS-CDMA Signals subject to Multipath Propagation