Ole Klein

Analysis of IEEE 802.11e for QoS support in wireless LANs

The IEEE 802.11e medium access control protocol is an emerging standard for wireless local area networks providing quality of service. An overview of this standard based on the current draft is presented on this article. We analyze the enhancements in 802.11 standard. The new hybrid coordination function of the IEEE 802.11e with its contention-based and contention-free (controlled) medium access control schemes is evaluated. The capability to provide QoS support is discussed by means of simulations.

Performance Evaluation of a Basic OFDMA Scheduling Algorithm for Packet Data Transmissions

Currently, the OFDMA transmission scheme seems to be a promising candidate for future broadband radio systems. The crucial part which determines the performance is thereby the combination of dynamic subcarrier allocation, transmission power allotment, and adaptive modulation. In this paper, the general effects of OFDMA scheduling concerning QoS for packet based data transmissions are described. Based on that information a basic scheduling algorithm which provides both fairness and exploitation of multiuser diversity is proposed for the deployment in centrally controlled systems like IEEE 802.16. Furthermore, a detailed performance evaluation of the algorithm is given for an exemplary scenario. The results show the impacts of multi-user diversity regarding packet delay and capacity.

Relay-based vs. Conventional Wireless Networks: Capacity and Spectrum Efficiency

Conventional radio cells suffer from the disadvantageous distribution of the transmission rates. High transmission rates are only available in the close vicinity of the access point, whereas the distribution of mobile stations behaves complementary. Hence, the provided capacity of the access point is only partly used and the majority is wasted. This drawback will grow with the introduction of future transmission techniques, which increase the maximum transmission rates available at short distances. Therefore, it is unlikely that the traditional design of cellular radio systems can achieve the ambitious throughput and coverage requirements of fourth- generation (4G) radio networks. We propose to extend conventional multi-cellular systems by applying relay-enhanced topologies to each cell. To encourage this evolutionary step we present an analytical model to compute the upper bound capacity and the spectrum efficiency of wireless networks. Based on this analytical model the potential of conventional cellular systems is compared with relay-enhanced networks.

Simulative MAC Level Performance Evaluation of an OFDMA System Under the Consideration of Frequency Correlated Fading

This paper is focused on the performance evaluation of OFDMA systems under the consideration of frequency correlated subchannel fading. A comprehensive model for the generation of correlated fading processes is proposed for the application in MAC level simulations. In contrast to most works in the research field of OFDMA, with this approach it is possible to conduct performance evaluations which incorporate both the traits of the medium access control scheme and of the physical layer. To approve the importance of considering correlation properties of the subchannels fading in an OFDMA system, a centrally controlled system based on IEEE 802.16 is analyzed in detail by means of stochastic event-driven simulations.

Frame descriptor tables for minimized signaling overhead in beyond 3G MAC protocols

In this paper we assess the performance of the frame descriptor tables (FDT) concept applied in combination with a highly dynamic resource allocation scheme. Beyond 3G (B3G) medium access control protocols (MAC) have to meet challenging requirements. In order to support the need for quality of service (QoS) and considering the scarce availability of radio resources, B3G MAC protocols must implement an intelligent resource allocation strategy with minimum signaling overhead guaranteeing high spectral efficiency. In this context the FDT concept seems to be a promising candidate. By eliminating redundant description of frame contents across frames the concept helps to reduce signaling overhead in a frame based reservation scheme. To keep as much flexibility as needed it seems reasonable to apply the FDT concept in combination with a highly dynamic resource allocation scheme. Simulations done in the course of this work prove the high quality of this combined approach

MAC Level Performance Evaluation of Downlink Resource Allocation Strategies for an OFDMA System Based on IEEE 802.16

In this paper, different downlink resource allocation strategies for an OFDMA are analyzed in detail. The performance of a centrally controlled system based on IEEE 802.16 is investigated by means of stochastic event-driven simulations. The focus is on the tradeoff between system capacity maximization due to the exploitation of multi user diversity and fairness in terms of packet delay. Since QoS (quality of service) provision is a critical design issue in the development of future broadband radio systems, the presented results can be considered as a contribution to the design process of such systems.

Efficient Multi-hop Communication in Beyond 3G Mobile Radio Networks

We propose and evaluate the Frame Descriptor Table (FDT) concept, a method to increase efficiency of signalling resource allocation in frame based Medium Access Control (MAC) protocols. MAC protocols for Beyond 3G mobile radio networks, also known as IMT-Advanced systems, will operate on high data rate channels resulting in short packet transmission duration. The scheduling overhead per packet must also be reduced, correspondingly. The new concept is suitable also to reduce the MAC control overhead spent per hop in mobile radio systems with Relay Enhanced Cells (REC)s that apply multi-hop communication by dynamically allocating TDMA channels. This paper’s focus is on performance evaluation of multi-hop scenarios using analytical models and event-driven stochastic simulations. It is shown that FDT based MAC protocols are suited to increase throughput and reduce delay in REC based cellular radio systems.

Performance evaluation of joint downlink scheduling in multi-cellular OFDMA systems based on IEEE 802.16a

The employment of the OFDMA transmission technique in broadband radio systems shows several benefits. Especially the exploitation of multi-user diversity with the help of sophisticated scheduling algorithms can significantly increase the system capacity. In this paper, the performance of joint scheduling of downlink data transmissions for access point sets is evaluated in a multi-cellular system. The latter is compared with an independent scheduling on orthogonal subchannel sets in the access points. The general MAC structure of the investigated system is thereby based on IEEE 802.16a. However, concerning the Physical Layer there is an important difference. In IEEE 802.16a, the exploitation of multi-user diversity is not possible since the OFDMA subchannel scheme is based on an interference and fading averaging approach. The technique examined in this paper in contrast can be regarded as an avoidance approach which is subject to diversity in the subchannel quality. A basic OFDMA scheduling algorithm, which is able to exploit multi-user diversity and provide fairness, is used both for the joint and for the independent scheme.

On the Minimization of Overhead in Relay Enhanced Mobile Radio Networks

In this paper, the Frame Descriptor Table (FDT) concept, invented to enable MAC protocols applying a frame based reservation strategy to cope with the requirements of 4G mobile radio networks, is evaluated concerning its efficiency in Relay Enhanced Cell (REC) scenarios. MAC protocols for 4G mobile radio networks, also known as IMT-Advanced systems, will operate on high data rate channels resulting in short packet transmission duration. With the help of the FDT concept the resulting increased overhead can be reduced and thus the MAC protocol is able to work in a highly efficient way. To improve the multi-hop communication applied in mobile radio systems with RECs the minimization of overhead is of particular importance. Based on analytical calculations in this paper it is shown that FDTs are very well suited to minimize the overhead in RECs and therefore are a means to enable MAC protocols meeting the demands expected from 4G mobile radio networks.