A Cross-Layer Two-Stage Scheduler for Wireless LANs

Abstract.A cross-layer wireless LAN system is considered which transmits packets for a number of users simultaneously using OFDMA or SDMA transmission. Due to varying packet lengths and physical bitrates for each user, this results in different transmission times so that users with faster transmissions have to wait until the transmission of the slower users is complete. Packet aggregation can reduce the loss of airtime and enhance the throughput without affecting the delay by filling in the gaps with additional packets which are ready for transmission. In this paper, the throughput is determined analytically and by simulation with and without packet aggregation for some given distribution functions of the packet size and the transmission time. For a more realistic channel model, the throughput enhancement due to packet aggregation is determined by simulations. It is shown that dependent on the distribution of the different flows, a significant throughput enhancement can be achieved.

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“…f max can be calculated according to (1) to (4), where x i = P i /R, P i being the size of the packet of flow i which is currently transmitted.…”

Section: Calculation Of the Throughputmentioning

confidence: 99%

“…The general concept of the system was introduced in [1] and extended by QoS support in [2]. In each turn of the scheduling process, the MAC scheduler assigns a priority to the data packet at the top of each queue according to throughput and delay requirements of the application.…”

Section: Introductionmentioning

confidence: 99%

Performance Analysis of Packet Aggregation in WLANs with Simultaneous Multi-user Access

Könsgen

Islam

Timm‐Giel

et al. 2009

Lecture Notes in Computer Science

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“…The first approach to meet these requirements was a twolayer scheduler which was proposed in [1]. The upper layer is located in the MAC layer and selects packets according to QoS requirements based on a certain scheduling strategy which can be selected out of different options.…”

Section: Introductionmentioning

confidence: 99%

An Enhanced Cross-Layer Two-Stage Scheduler for Wireless LANs

Könsgen

Herdt

Wang

et al. 2007

2007 IEEE 18th International Symposium on Personal, Indoor and Mobile Radio Communications

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In this paper, a QoS-aware cross-layer scheduler for wireless LANs is introduced which allows the control of a number of data flows according to QoS requirements of the respective applications. It is based on a two-stage concept: The MAC layer scheduler uses an importance function to calculate the priority of a particular flow, whereas the PHY layer scheduler considers the channel conditions of a MIMO-TDMA transmission. It is shown that with the concept presented here, throughput and delay requirements of time-critical applications can be met.

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“…To cope with these requirements, in the framework of the xLAYER project funded by the German Research Foundation (DFG), a cross-layer transmission system for wireless LANs was introduced in [9] and extended by QoS support in [10]; the OFDMA/SDMA platform which means the parallel transmission to multiple users was introduced in [5].…”

Section: Introductionmentioning

confidence: 99%

“…Fig. 1 shows the design of the cross-layer scheduler introduced in [9] which is used for the investigations described in this paper. The scheduler includes a hardwareindependent stage in the MAC layer and a hardware-dependent stage in the PHY layer.…”

Section: Introductionmentioning

confidence: 99%

Optimization of a QoS Aware Cross-Layer Scheduler by Packet Aggregation

Könsgen

Islam

Timm‐Giel

et al.

Wireless and Mobile Networking

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In this paper, the performance of a QoS-aware two-stage cross-layer scheduler utilising a MIMO channel for transmission is considered along with TDMA, OFDMA and SDMA channel access methods which serves a number of users with QoS-constrained data flows. OFDMA and SDMA allow a parallel transmission of packets which can have different transmission durations due to varying physical bit rates and packet lengths. The data flow with the longest packet slows down the other flows because they have to wait until the transmission is complete. This paper proposes packet aggregation where waiting times are reduced by transmitting more than one packet per user if airtime is left. It is shown that this method significantly enhances the QoS parameters throughput and delay. For constant-size packets, shorter delays can be achieved than for variable-size packets. Aggregating non-consecutive packets further enhances the performance, however the packets have to be buffered at the receiver to put them into the correct order. IntroductionWireless LANs have to meet increasing requirements nowadays and in the future: high data rates for each user, high spectral efficiency in the sense of a high total capacity and meeting several types of QoS requirements for different applications.Up to now, most protocols stacks are designed according to the OSI model which defines seven layers from the physical layer up to the application layer, with an increasing degree of abstraction from the physical hardware. In legacy protocol stacks, these different protocol layers have been optimised independently of each other. This separation is in particular problematic for the design of the two lowest layers, which are the MAC and the PHY layer, because there are close mutual dependencies between these two layers. The QoS requirements have already to be considered by selecting the physical transmission method. Moreover, the actual channel conditions and the effects of these conditions for a QoS aware transmission have to be known when selecting a particular packet for the transmission.Please use the following format when citing this chapter:

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A Cross-Layer Two-Stage Scheduler for Wireless LANs

Cited by 4 publications

References 6 publications

Performance Analysis of Packet Aggregation in WLANs with Simultaneous Multi-user Access

Performance Analysis of Packet Aggregation in WLANs with Simultaneous Multi-user Access

An Enhanced Cross-Layer Two-Stage Scheduler for Wireless LANs

Optimization of a QoS Aware Cross-Layer Scheduler by Packet Aggregation

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