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

In order to achieve up to 1 Gb/s peak data rate in future IMT-Advanced mobile systems, carrier aggregation technology is introduced by the 3GPP to support very-high-data-rate transmissions over wide frequency bandwidths (e.g., up to 100 MHz) in its new LTE-Advanced standards. This article first gives a brief review of continuous and non-continuous CA techniques, followed by two data aggregation schemes in physical and medium access control layers. Some technical challenges for implementing CA technique in LTE-Advanced systems, with the requirements of backward compatibility to LTE systems, are highlighted and discussed. Possible technical solutions for the asymmetric CA problem, control signaling design, handover control, and guard band setting are reviewed. Simulation results show Doppler frequency shift has only limited impact on data transmission performance over wide frequency bands in a high-speed mobile environment when the component carriers are time synchronized. The frequency aliasing will generate much more interference between adjacent component carriers and therefore greatly degrades the bit error rate performance of downlink data transmissions.

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Carrier aggregation for LTE-advanced mobile communication systems

Methods of mapping, indicating, encoding and transmitting uplink (UL) grants and downlink (DL) assignments for wireless communications for carrier aggregation are disclosed. Methods to encode and transmit DL assignments and UL grants and map and indicate the DL assignments to DL component carriers and UL grants to UL component carriers are described. Methods include specifying the mapping rules for DL component carriers that transmit DL assignment and DL component carriers that receive physical downlink shared channel (PDSCH), and mapping rules for DL component carriers that transmit UL grants and UL component carriers that transit physical uplink shared channel (PUSCH) when using separate coding/separate transmission schemes.

Uplink grant, downlink assignment and search space method and apparatus in carrier aggregation

A method and an apparatus of receiving data in a wireless communication system are provided. The method includes detecting a physical downlink control channel (PDCCH) on which control information is transmitted in a first subframe, and receiving data in at least one second subframe based on the control information.

Method and apparatus of receiving data in wireless communication system

A base station includes transmitter and associated processing circuits. The transmitter circuits are configured to transmit control information and data traffic to mobile terminals in repeating transmission intervals, each interval having defined control and data portions. The processing circuits are configured to dynamically determine that the control portion has insufficient resources for transmitting control information to one or more of the mobile terminals, and, in response, at least temporarily transmit control information in the data portion, rather than in the control portion, for a selected one or more of the mobile terminals. Correspondingly, a mobile terminal is configured to selectively search for and decode control information in the data portion of one or more transmission intervals, rather than in the control portion.

Method and apparatus for robust transmission of control information in a wireless communication network

With the emergence of packet-based wireless broadband systems, work has begun on long term evolution (LTE) of the UMTS Terrestrial Radio Access and Radio Access Network aimed for commercial deployment in 2010. Goals for the evolved system include support for improved system capacity and coverage, high peak data rates, low latency, reduced operating costs, multi-antenna support, flexible bandwidth operations and seamless integration with existing systems. To reach these goals, a new design for the air interface including control channel is envisioned. This paper provides a preliminary look at an efficient downlink control channel design to reduce the overhead required to support data transmission. Initial performance results show that close to optimal system performance can be achieved with downlink control overhead of less than 14%.

Downlink Control Channel Design for 3GPP LTE

Enhanced uplink technology is currently being considered for standardization in 3GPP W-CDMA (Release-6) with the standard scheduled for completion in the 4/sup th/ quarter of 2004. Enhanced uplink technology under consideration includes advanced techniques such as adaptive modulation and coding (AMC), hybrid ARQ (HARQ), fast rate control or fast scheduling by the node-B (base station), higher peak rates (up to 2 Mbps) and a reduced transition latency between CELL_DCH, CELL_FACH and CELL_PCH states. These techniques reduce overall delay, and increase throughput significantly compared to release-99/4/5 3GPP W-CDMA. In this paper, the physical layer aspects of enhanced uplink for 3GPP W-CDMA FDD are discussed in detail with accompanying link and system simulation results. These results show that the sector and user throughput of the enhanced uplink (EU) can be improved by more than 50% compared to release-99/4/5 3GPP W-CDMA.

Overview of enhanced uplink for 3GPP W-CDMA

Evolved UTRA (EUTRA) is currently under study by 3GPP standards organizations as a long term evolution (LTE) for current generation universal terrestrial radio access (UTRA) networks. One of the key aspects of EUTRA wireless systems will be providing voice services in packet domain using voice over IP (VoIP). This paper provides system simulation results evaluating uplink VoIP capacity for EUTRA. Simulations indicate that if efficient control signaling and scheduling mechanisms are in place, EUTRA systems can support 80 to 130 Erlangs of VoIP traffic per sector in a 1.08 MHz spectrum allocation as part of a 5 MHz LTE carrier.

R. Kuchibhotla

Papers

Downlink Control Channel Design for 3GPP LTE

Overview of enhanced uplink for 3GPP W-CDMA

Uplink VoIP Support for 3GPP EUTRA