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

Abstract

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:

Optimized packet formation in multi‐level security wireless data acquisition networks

“…A physical layer schedule then picks packets from the queue according to their latency-based priority while factoring in the channel conditions to maximize the bit rate. The idea is further extended in Reference [13] to expedite the packet transmissions of fast flows by piggybacking packets according to the channel condition and the remaining portion of the allotted time.…”