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 first communication node ( 110 ) receives a stream of code blocks from a second communication node ( 120 ) over an acknowledged connection ( 131. ). The first communication node processes the received code blocks in accordance with at least one transport format parameter, TFP, detects errors in received code blocks, and transmits an acknowledgment in respect of groups of code blocks indicating whether at least one error was detected in the group. A first subset of the code blocks of a group are transmitted (e.g., modulated and demodulated) in accordance with a first TFP value, and a remainder of the code blocks are transmitted in accordance with a second TFP value. Because the first and second TFP values are independent, it is possible either to shorten the necessary processing time in the first communication node or, in connection with a predictive acknowledgment mechanism, to make the receiving-side processing of code blocks that do not contribute to the value of the transmitted acknowledgment more robust.

Variable Transport Format Parameters for Fast Acknowledgment Feedback Mechanism

A first and a second radio communication device and a respective method performed thereby for communicating between the first and the second radio communication device are provided. The method in the first radio communication device comprises transmitting, on an unlicensed frequency band, to at least the second radio communication device, an indication of a duration of a guard period, wherein an upcoming data transmission is to be performed to the second radio communication device after the expiration of the guard period. The method further comprises during the guard period, sending and/or receiving information to/from at least one other radio communication device, the other communication device being the second radio communication device or a third communication device.

Radio devices and methods for performing communication via licensed and unlicensed spectrum

A communications system comprises a terminal, and network resources. The terminal is operable to transmit substantially simultaneously a data portion and a data transfer request for that data portion to the network resources.

Communications system and method for transmitting data between a terminal and network resources

The performance of cellular DS-CDMA systems using long and short spreading sequences is compared in terms of bit error probability, and both conventional and MMSE detectors are considered. A slightly higher performance variability is found for the short code case and code hopping as a technique to mitigate this is investigated.

Long vs short spreading codes in cellular DS-CDMA

Publisher Summary This chapter deals with some radio-resource-management issues, including uplink power control, downlink and uplink scheduling, and different means for intercell interference coordination to handle/avoid severe interference between different cells including cells of different layers in heterogeneous network deployments. Uplink power control for LTE is the set of algorithms and tools by which the transmit power for different uplink physical channels and signals are controlled to ensure that they, if possible, are received at the cell site with appropriate power. This means that the transmission should be received with sufficient power to allow for proper demodulation of the corresponding information. At the same time, the transmit power should not be unnecessarily high as that would cause unnecessary interference to other cells. The transmit power will thus depend on the channel properties, including the channel attenuation and the noise and interference level at the receiver side. This chapter begins with elaborating the basic rules of uplink power control, power control for PUCCH, power control for PUSCH and SRS. It then discusses the downlink scheduling, uplink scheduling, semipersistent scheduling, and scheduling for half-duplex FDD. The chapter concludes with a discussion on intercell interference coordination and heterogeneous network deployments.

Stefan Parkvall

Papers

Variable Transport Format Parameters for Fast Acknowledgment Feedback Mechanism

Radio devices and methods for performing communication via licensed and unlicensed spectrum

Communications system and method for transmitting data between a terminal and network resources

Long vs short spreading codes in cellular DS-CDMA

Power Control, Scheduling, and Interference Handling