Future generation cellular networks are expected to provide ubiquitous broadband access to a continuously growing number of mobile users. In this context, LTE systems represent an important milestone towards the so called 4G cellular networks. A key feature of LTE is the adoption of advanced Radio Resource Management procedures in order to increase the system performance up to the Shannon limit. Packet scheduling mechanisms, in particular, play a fundamental role, because they are responsible for choosing, with fine time and frequency resolutions, how to distribute radio resources among different stations, taking into account channel condition and QoS requirements. This goal should be accomplished by providing, at the same time, an optimal trade-off between spectral efficiency and fairness. In this context, this paper provides an overview on the key issues that arise in the design of a resource allocation algorithm for LTE networks. It is intended for a wide range of readers as it covers the topic from basics to advanced aspects. The downlink channel under frequency division duplex configuration is considered as object of our study, but most of the considerations are valid for other configurations as well. Moreover, a survey on the most recent techniques is reported, including a classification of the different approaches presented in literature. Performance comparisons of the most well-known schemes, with particular focus on QoS provisioning capabilities, are also provided for complementing the described concepts. Thus, this survey would be useful for readers interested in learning the basic concepts before going into the details of a particular scheduling strategy, as well as for researchers aiming at deepening more specific aspects.

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Downlink Packet Scheduling in LTE Cellular Networks: Key Design Issues and a Survey

Orthogonal Frequency Division Multiplexing Access (OFDMA) has been increasingly deployed in various emerging and evolving cellular systems to reduce interference and improve overall system performance. However, in these systems Inter-Cell Interference (ICI) still poses a real challenge that limits the system performance, especially for users located at the cell edge. Inter-cell interference coordination (ICIC) has been investigated as an approach to alleviate the impact of interference and improve performance in OFDMA-based systems. A common ICIC technique is interference avoidance in which the allocation of the various system resources (e.g., time, frequency, and power) to users is controlled to ensure that the ICI remains within acceptable limits. This paper surveys the various ICIC avoidance schemes in the downlink of OFDMA-based cellular networks. In particular, the paper introduces new parameterized classifications and makes use of these classifications to categorize and review various static (frequency reuse-based) and dynamic (cell coordination-based) ICIC schemes.

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A Survey on Inter-Cell Interference Coordination Techniques in OFDMA-Based Cellular Networks

With the power consumption issue of mobile handset taken into account, single-carrier FDMA (SC-FDMA) has been selected for 3GPP long-term evolution (LTE) uplink multiple access scheme. Like in OFDMA downlink, it enables multiple users to be served simultaneously in uplink as well. However, its single carrier property requires that all the subcarriers allocated to a single user must be contiguous in frequency within each time slot. This contiguous allocation constraint limits the scheduling flexibility, and frequency-domain packet scheduling algorithms in such system need to incorporate this constraint while trying to maximize their own scheduling objectives. In this paper we explore this fundamental problem of LTE SC-FDMA uplink scheduling by adopting the conventional time-domain proportional fair algorithm to maximize its objective (i.e. proportional fair criteria) in the frequency-domain setting. We show the NP-hardness of the frequency-domain scheduling problem under this contiguous allocation constraint and present a set of practical algorithms fine tuned to this problem. We demonstrate that competitive performance can be achieved in terms of system throughput as well as fairness perspective, which is evaluated using 3GPP LTE system model simulations.

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Proportional Fair Frequency-Domain Packet Scheduling for 3GPP LTE Uplink

The challenge of scheduling user transmissions on the downlink of a long term evolution (LTE) cellular communication system is addressed. A maximum rate algorithm which does not consider fairness among users was proposed in . Here, a multiuser scheduler with proportional fairness (PF) is proposed. Numerical results show that the proposed PF scheduler provides a superior fairness performance with a modest loss in throughput, as long as the user average SINRs are fairly uniform. A suboptimal PF scheduler is also proposed, which has a much lower complexity at the cost of some throughput degradation.

Proportional Fair Multiuser Scheduling in LTE

Systems and methods for providing broadband internet access to mobile platforms such as vehicles, aircraft, and portable devices, using a network of one or more entities such as drones/unmanned aerial vehicles (UAVs). In one embodiment, the drone communication system comprises an antenna sub-system, a radio sub-system and a data switching sub-system. The mobile platforms comprise antenna and radio sub-systems to communicate with the drones, detect changes in the mobile platforms azimuth and elevation changes, and adjust the mobile platform's antenna beam to compensate for the orientation changes to optimally point toward the drones. The exemplary mobile platform further comprises methods to detect the need for handoff to a different drone and to carry out the handoff. A mechanism to improve coverage to mobile platforms that may see obstruction on their path to the drone network is also disclosed, as are apparatus and methods for cost efficiently providing reliable internet access to portable devices.

Broadband access to mobile platforms using drone/uav background

In this paper, a generalized proportional fair (GPF) scheduling algorithm is presented, which allows tweaking the trade-off between fairness and throughput performance for best effort traffic in a cellular downlink scenario. The GPF is extended to frequency scheduling in an OFDMA system by performing dynamic channel allocation on a subband basis including link adaptation by adaptive modulation and coding. In this way, multiuser diversity can be utilized in time domain - as for CDMA - and in frequency domain. Compared to a system without frequency scheduling, this increases the system throughput and yields an improved fairness with respect to the allocated resources and with respect to the achieved data-rate per user. OFDMA system level simulations are carried out in order to analyze short/long-term fairness, multiuser diversity gain and system throughput of various GPF configurations with and without applying frequency scheduling.

Fairness and throughput analysis for generalized proportional fair frequency scheduling in OFDMA

A method is described for scheduling a plurality of data flows to a plurality of shared channels in a wireless communication system transmitting data packets in time intervals of frames and applying adaptive modulation and coding. The method comprises the steps of determining virtual link adaptation parameters for at least a part of all combinations of data flow and shared channel, based on state information from the respective shared channel, and based on Quality of Service requirements for the respective data flow; calculating potential data rates for said combinations of data flow and shared channel, based on said virtual link adaptation parameters; calculating priority values for said combinations of data flow and shared channel, based on said potential data rates; and selecting, based on the calculated priority values, for at least a part of the shared channels, a data flow for which data is to be transmitted on each of these shared channel during the time interval of one frame.

Scheduling depending on quality of service and channel properties

The present disclosure relates to transmitting transport blocks in subframes of a predefined length within a wireless communication system. A downlink control information including a resource grant comprising a predetermined modulation and a predetermined transport block size is received (user equipment is the transmitter) or generated (base station is the transmitter). Then transport block including channel coded data to be transmitted in a subframe with the predetermined modulation and the predetermined transport block size is generated. Sensing is performed in the subframes and based thereon, it is determined whether a partial subframe or a complete subframe is available for transmission of the generated transport block. Finally, the transport block is transmitted with a modified modulation different from the predetermined modulation if the partial rather than complete subframe is available. Correspondingly, at the receiver, the grant is received (user equipment is receiver) or generated (base station is the receiver), the size of the subframe in which the reception is expected is determined and then the transport block is received with a modified modulation if only the partial subframe is available.

Modulation order adaptation for partial subframes

The present disclosure relates to a method for transmitting and receiving a beamformed data transmission transmitted from a radio base station to a user equipment over an unlicensed band. The data transmission is transmitted by the radio base station within one or more resource blocks of a subframe, each resource block being composed of a plurality of resource elements. The beamformed data transmission is generated by the radio base station by 1) applying a first precoding for generating a beam directionality towards the user equipment to a subset of all the resource elements used for transmitting the data transmission in the subframe, and 2) applying a second precoding, different from the first precoding, to the remaining resource elements used for transmitting the data transmission in the subframe so as to achieve a radiation pattern different from the beam directionality towards the user equipment.

PDSCH precoding adaptation for LTE in unlicensed bands

The invention relates to a radio base station or user equipment for scheduling respectively performing uplink transmissions via an unlicensed cell configured between the user equipment and the radio base station. The UE can perform an uplink transmission via the unlicensed cell according to at least the following types. A first type spans a complete subframe duration and starts and ends at subframe boundaries followed by the UE. A second type spans a complete subframe duration and includes an additional time offset with respect to the subframe boundaries followed by the UE. A third type spans less than a complete subframe duration and includes an additional time offset with respect to the subframe boundaries followed by the UE. The UEs perform uplink transmissions according to one of the types in such a manner that at least between two directly-subsequent uplink transmissions a time gap with no uplink transmission occurs.

Jan Ohlhorst

Papers

Fairness and throughput analysis for generalized proportional fair frequency scheduling in OFDMA

Scheduling depending on quality of service and channel properties

Modulation order adaptation for partial subframes

PDSCH precoding adaptation for LTE in unlicensed bands

Improved uplink transmissions in unlicensed cells with additional transmission timing offsets