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 invention discloses a method for a cellular communications system, in which traffic is sent in frames, each frame comprising a first number of subframes, with a second number of said subframes being available for at least either uplink or downlink traffic. At least one of said second number of subframes is made to comprise at least three parts, as follows:
 One part which is utilized for uplink traffic, One part which is utilized for downlink traffic, One part which is utilized as a guard period,
 
with said guard period part being scheduled between the uplink and the downlink parts. The duration of at least two of said three parts may be varied to fit the current system need.

TDD time slot splitting

In one aspect, a wireless device receives a first data transmission from a base station during a predetermined subframe interval and within a duration that is less than a maximum data transmission duration that is possible within the predetermined subframe interval, and determines a transmission time for transmitting HARQ feedback to the base station such that the determined transmission time depends on which subset of symbols within the predetermined subframe interval was used for the first data transmission. The wireless device transmits HARQ feedback for the first data transmission at the determined transmission time. In another aspect, a base station transmits the first data transmission and determines a reception time for receiving HARQ feedback such that the determined transmission time depends on which subset of symbols within the predetermined subframe interval was used. The base station receives HARQ feedback for the first data transmission at the determined transmission time.

Sub-subframe assignment and harq timing

The invention relates to a method (90) in a user equipment (4) for reporting a downlink channel quality in a communication system (1) comprising a first radio access technology system (2) and a second radio access technology system (3). The user equipment (4) is in connection with a primary serving cell on the first radio access technology system (2) and with a secondary serving cell on the second radio access technology system (3). The method (90) comprises: determining (110) channel quality for the second radio access technology system (3) using an indicator format of the radio access technology of the second radio access technology system (3); mapping (120) an indicator of the channel quality having the indicator format of the second radio access technology to an indicator format used for channel quality indicators in the first radio access technology system (2); and transmitting (130) the indicator of the channel quality for the second radio access technology system (3) to the communication system (1) using the indicator format of the first radio access technology on an uplink carrier of the first radio access technology system (2). The invention also relates to a user equipment, methods in a network node and a network node.

Methods and devices for reporting a downlink channel quality

The present invention relates to a first node and a second node in a mobile telecommunication network. The network comprises a first node, a second node and a third node, wherein the first node is connectable to the second node and the second node is connectable to the first node and to the third node and the third node is connectable to the second node. A system function is realized by the execution of a master-process implemented in the first node and a slave-process implemented in the third node, and wherein the execution of the master-process realizes a control function associated with the system function. The master-process of the first node is adapted to temporarily delegate the responsibility to realize the control function to a master-proxy-process implemented in the second node and the master-proxy-process implemented in the second node is adapted to take over the responsibility to realize the control function from the master-process of the first node.

Arrangements in a mobile telecommunication network

A network node operates in accordance with a first radio access technology in a frequency band, wherein communication according to a second radio access technology may occupy one or more of the radio resources of the frequency band. A method comprises receiving a beacon signal associated with the second radio access technology and determining whether or not the beacon signal comprises information indicative of which of the radio resources of the frequency band are used as primary and secondary channels, respectively, in accordance with the second radio access technology. The method also comprises determining a communication activity rate of at least one of the radio resources of the frequency band and selecting one or more of the radio resources of the frequency band based on the determined communication activity rate, and allocating one or more of the selected radio resources to communication in accordance with the first radio access technology.

Stefan Parkvall

Papers

TDD time slot splitting

Sub-subframe assignment and harq timing

Methods and devices for reporting a downlink channel quality

Arrangements in a mobile telecommunication network

Radio resource allocation of unlicensed frequency bands