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

The mobile Internet that will be enabled by LTE-Advanced Pro and the way in which we interact with it will change significantly within the next few years. From a usage point of view, it is anticipated that by 2020, each person, globally speaking, will consume on average as much as 5 GB of data each month, in addition to the traffic generated by 20-30 billion connected things. More significantly, not only will the mobile network be significantly faster, but even more applications will become possible. The video experience will be improved globally; mobile virtual reality will be available; networked vehicles and perhaps self-driving cars will roam our streets; the Internet of Things will enrich and make our lives more productive; and a mobile cloud will allow access to our data anytime, anywhere.

LTE-Advanced Pro: Part 3 [Guest Editorial]

According to some embodiments, a method for use in a wireless transmitter of a wireless communication network comprises providing control information relating to a slot. The control information includes an indication of whether the slot is of a first type or a second type. A slot of the first type starts at a slot interval boundary, and a slot of the second type either starts between slot interval boundaries and has arbitrary length or starts at a slot interval boundary and has reduced length. The control information includes an implicit or explicit reference signal timing indication if the slot is of the second type. The method further comprises transmitting the control information to a wireless receiver.

Signaling Reference Signal Locations in Slots and Mini-Slots

The teachings presents a method 10 performed in a network node 2, the network node 2 controlling a first and a second antenna point 3, 4. The network node 2 uses the same random access resources for the first and the second antenna points 3, 4. The method 10 comprises: detecting 11 a specific random access preamble received on a random access resource at the first antenna point 3 and on the same random access resource at the second antenna point 4; and scheduling 12 a transmission of a random access response to the random access preamble received at the first antenna point 3 and a transmission of a random access response to the random access preamble received at the second antenna point 4, the random access responses being scheduled separated in time and/or space. The teachings also presents corresponding devices.

Methods and devices for controlling antenna points

The uplink performance in a cellular DS-CDMA systems using long and short spreading sequences is compared in terms of the distribution of the bit error probability, both with and without forward error correction. Two different receiver types are considered, conventional and MMSE, both with and without forward error correction. The short code system has a slightly higher performance variability among the user population than the corresponding long code system, which requires attention when designing a short code system. Code hopping as a technique to mitigate this is investigated.

User performance variability in DS-CDMA systems-long vs. short spreading sequences

Methods and apparatuses disclosed herein enable the use of Demodulation Reference Signal, DMRS, sequences that are numbered relative to an overall system bandwidth (30), while simultaneously enabling wireless communication devices (12) to determine the DRMS sequence elements mapped to their scheduled bandwidths (36) within the system bandwidth (30). Advantageously, the wireless communication devices (12) need not know the system bandwidth (30), or even be aware of where their scheduled bandwidths (36) reside within the system bandwidth (30).

Stefan Parkvall

Papers

LTE-Advanced Pro: Part 3 [Guest Editorial]

Signaling Reference Signal Locations in Slots and Mini-Slots

Methods and devices for controlling antenna points

User performance variability in DS-CDMA systems-long vs. short spreading sequences

Methods and apparatuses for signaling and determining reference signal offsets