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

Techniques are disclosed for allocating time-frequency resources in a system that uses multiple multicarrier modulation numerologies. According to one aspect, a method in a first wireless node comprises allocating (1310) time-frequency resources for use by a second wireless node, where said allocating comprises selecting, for use in multicarrier modulation in the allocated time-frequency resources, one of two or more subcarrier bandwidths that the second wireless node is adapted to use for modulating or demodulating of data. In some embodiments, the method further comprises sending (1320) resource allocation information to the second wireless node, the resource allocation information identifying the allocated time-frequency resources.

Resource allocation for data transmission in wireless systems

We present the potential performance improvements attainable by new enhancements to the WCDMA uplink. Improvements can be expected in both system capacity and end-user perceived performance. In this paper we focus on the capacity gains of short TTI, hybrid ARQ and scheduling in node-B. The performance is studied from both the link-level and system-level perspectives. The link performance results focus on the gains obtained by the introduction of short TTI and hybrid ARQ with soft combining in node-B. In the system performance results, we also evaluate node-B based rate scheduling for both 2 ms TTI and 10 ms TTL. Our studies indicate that with the introduction of enhanced uplink the gain in uplink capacity can be in the order of 70-100%.

System performance of WCDMA enhanced uplink

The embodiments of the present invention relate to apparatuses and methods for resource management in a multi-carrier system wherein a plurality of component carriers (CCs) is defined per cell. According to a method in an apparatus corresponding to a radio base station, a message is assembled comprising information on the structure of the cell served by the radio base station; the information including one or more CCs used in the cell that is/are available for a user equipment for performing initial access in the cell. The method also comprises, transmitting the assembled message to the user equipment and indicating to the user equipment to what resources to use for random access in the cell. The exemplary embodiments of the present invention also relates to a method in the user equipment, to a radio base station and to a user equipment.

Methods and apparatus for resource management in a multi-carrier telecommunications system

The present invention relates to a user terminal, UE, in a wireless communication system (1). The user terminal (4a, 4b) comprisesa receiver unit(5a, 5b), a transmitter unit(6a, 6b) configured to transmit data in transmit sub-frames occurring at defined sub-frameintervals, and a control unit(7a, 7b) configured to control the receiver circuit (5a, 5b) andthetransmitter circuit (6a, 6b).The control unit(7a, 7b) is alsoconfigured tocreate a PRACH, Physical Random-Access Channel, preamble (27) as an uplink transmission to a node (2) that is arranged to receive communication from the user terminal in said sub-frames. This communication comprises OFDM, Orthogonal Frequency-Division Multiplexing, based symbols (20). The control unit(7a, 7b)is configured to create each PRACH preamble (27) such that is comprises a sequence of a plurality of identical random access sequences (s(n)), where each random access sequence (s(n)) has the same length in time as each one of the OFDM based symbols (20a, 20b, 20c). The present invention also relates to a corresponding method.

Enhanced PRACH preamble format

Network densification and heterogeneous deployments are key tools to satisfy future traffic-volume and end-user service-level demands. LTE release 10/11 introduced several features to enhance LTE operation in heterogeneous deployments. This will continue as part of the work on small-cell enhancements in LTE Release 12. Especially, different forms of dual-connectivity are being considered to improve overall system performance and enhance end-user experience.

Stefan Parkvall

Papers

Resource allocation for data transmission in wireless systems

System performance of WCDMA enhanced uplink

Methods and apparatus for resource management in a multi-carrier telecommunications system

Enhanced PRACH preamble format

Future wireless access small cells and heterogeneous deployments