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

Cell Search and System Information

One of the main targets for LTE is to provide significantly higher end-user data rates than previous systems. This chapter discusses some of the more fundamental constraints that exist in terms of what data rates can be achieved in different situations, followed by a discussion on means to increase the achievable data rates in different mobile-communication scenarios.

High data rates in mobile communication

Systems and methods are disclosed for transmission and reception of an uplink grant during a gap created in radio resources assigned by a previous multiple Transmit Time Interval (multi-TTI) uplink grant in a system operating according to a Time Division Duplexing (TDD) scheme. In one embodiment, a 5 method of operation of a radio network node (12) in a cellular communications network (10) is provided. The method includes transmitting a first uplink grant that assigns radio resources for a multi-TTI uplink transmission, and transmitting a second uplink grant during a gap in the radio resources assigned by the first uplink grant. In one embodiment, by utilizing the gap to transmit the second 10 uplink grant, uplink radio resources assigned for uplink transmission can be maximized, which is particularly beneficial in high uplink traffic conditions.

Efficient multi-tti scheduling for uplink tdd

A method (1200) for transmission of control data to a user equipment (904) in a mobile telecommunication system (900), wherein the method (1200) comprises sending (1220) control data to the user equipment (904) in a data transmission (600, 700, 800, 1300, 1400), and performing, by the user equipment (904), a blind decoding (1260) of transmission elements within the data transmission (600, 700, 800, 1300, 1400) in order to detect the control data in a data region (604) in the data transmission (600, 700, 800, 1300, 1400).

Transmission and reception of control data in a communication system

Selon l'invention, un emetteur pouvant presenter une disponibilite de puissance marginale peut retransmettre de maniere autonome des trames transmises precedemment contenant les memes donnees. L'emetteur envoie une trame initiale a une station d'emission-reception de base (BTS) et retransmet immediatement la meme trame independamment d'une quelconque transmission d'ACK/NAK de la BTS. Les retransmissions sont accumulees dans le recepteur et decodees apres transmission d'une quantite suffisante de la trame. Apres reception de la derniere trame retransmise, la BTS envoie un ACK/NAK a l'emetteur qui est accepte.

Stefan Parkvall

Papers

Cell Search and System Information

High data rates in mobile communication

Efficient multi-tti scheduling for uplink tdd

Transmission and reception of control data in a communication system

Procede et systeme pour assurer des retransmissions autonomes dans un systeme de communication sans fil