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

A base station transmits signals on a frequency (f1) in an active transmission interval (TI) having a starting time and being part of a transmission cycle (TC) including other active transmission intervals for other frequencies (f0, f1, f2, f3) appearing in a predetermined discontinuous transmission scheme that specifies the relationship (D1, Az, A3) between the starting times of the active transmission intervals of the frequencies of the set. The mobile station scans the set of frequencies during a scanning cycle (SC) corresponding to the transmission cycle (TC) and determines the frequencies at which the base stations transmit. The start of each scanning is made at a point in time that is specified for the corresponding frequency by the discontinuous transmission scheme and the scanning of one frequency involves ending scanning of this frequency at the end of a time range (TR) of pre-determined length if no signal is detected within this time range.

Discontinuous transmission scheme

Method and arrangement for allocating usable sub-carriers to physical resource blocks in a mobile telecommunications system

In this paper, the first step of evolving WCDMA beyond IMT-2000 is outlined and elaborated upon. It is shown how techniques such as fast link adaptation, fast hybrid ARQ and fast scheduling, among others, can be applied to WCDMA, leading to increased throughput for best-effort services, lower delays, and downlink peak rates in the order of 10 Mbit/s. The end-to-end protocol architecture is discussed, and using protocol simulations the benefit of having a hybrid type II ARQ scheme in Node B is shown.

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Enhancing Packet Data Access in WCDMA

A radio network controller, RNC, 614, and a method therein, for enhancing reception quality of transmissions on an uplink control channel from a user equipment, UE, 613 to a serving base station, BS, 610. The RNC, the UE and the serving BS are comprised in a communication system 600. The method comprises, when conditions for boosting the uplink control channel are fulfilled, determining a boosting factor based on a ratio of path gains of a channel from the UE to the serving BS and of a channel from the UE to a non- serving BS 611, respectively, which non-serving BS is comprised in the communications system. The method further comprises transmitting the determined boosting factor to the UE, whereby the reception quality of transmission on the uplink control channel from the UE to the serving BS is enhanced by the UE boosting the control channel by means of the boosting factor.

A Radio Network Controller, A Serving Base Station, A User Equipment and Methods Therein

The chapter describes the NR uplink power control and uplink timing control. The similarities and differences to the corresponding LTE mechanisms are high-lighted. Especially, the NR mechanisms for beam-based power control are high-lighted.

Stefan Parkvall

Papers

Discontinuous transmission scheme

Method and arrangement for allocating usable sub-carriers to physical resource blocks in a mobile telecommunications system

Enhancing Packet Data Access in WCDMA

A Radio Network Controller, A Serving Base Station, A User Equipment and Methods Therein

Uplink Power and Timing Control