Optimal Rate Sampling in 802.11 Systems

In 802.11 systems, Rate Adaptation (RA) is a fundamental mechanism allowing transmitters to adapt the coding and modulation scheme as well as the MIMO transmission mode to the radio channel conditions, and in turn, to learn and track the (mode, rate) pair providing the highest throughput. So far, the design of RA mechanisms has been mainly driven by heuristics. In contrast, in this paper, we rigorously formulate such design as an online stochastic optimisation problem. We solve this problem and present ORS (Optimal Rate Sampling), a family of (mode, rate) pair adaptation algorithms that provably learn as fast as it is possible the best pair for transmission. We study the performance of ORS algorithms in both stationary radio environments where the successful packet transmission probabilities at the various (mode, rate) pairs do not vary over time, and in non-stationary environments where these probabilities evolve. We show that under ORS algorithms, the throughput loss due to the need to explore sub-optimal (mode, rate) pairs does not depend on the number of available pairs, which is a crucial advantage as evolving 802.11 standards offer an increasingly large number of (mode, rate) pairs. We illustrate the efficiency of ORS algorithms (compared to the state-of-the-art algorithms) using simulations and traces extracted from 802.11 test-beds.Comment: 52 page

Adaptive thresholding based optimal rate and MIMO mode selection scheme for IEEE 802.11n WLAN

The emergence of multiple antenna technology in IEEE 802.11n WLAN  has resulted in performance improvement in terms of throughput as well as transmission reliability as compared to legacy standards. Link adaptive transmission is critical to WLAN. Most of the existing algorithms for MIMO mode adaptation (between spatial multiplexing and diversity encoding) use fixed SNR switching thresholds for rate selection. The use of a fixed threshold in both MIMO modes, however, can only provide smaller throughput gain. The present studies on link adaptation do not consider the fundamental characteristic difference in the diversity encoding and spatial multiplexing encoding for MIMO. In this paper we propose a novel adaptive thresholding based optimal rate and MIMO mode (ORMM) algorithm for 802.11n wireless network. The proposed scheme adaptively switches between two SNR switching threshold vectors, separately determined for each MIMO mode analytically. Simulations over the Rayleigh fading channel shows that ORMM outperforms the existing approach of MIMO rate adaptation based on the use of fixed switching thresholds for rate selection

IEEE 802.11n MAC frame aggregation mechanisms for next-generation high-throughput WLANs [Medium access control protocols for wireless LANs]

IEEE 802.11n is an ongoing next-generation wireless LAN standard that supports a very highspeed connection with more than 100 Mb/s data throughput measured at the medium access control layer. This article investigates the key MAC enhancements that help 802.11n achieve high throughput and high efficiency. A detailed description is given for various frame aggregation mechanisms proposed in the latest 802.11n draft standard. Our simulation results confirm that A-MSDU, A-MPDU, and a combination of these methods improve extensively the channel efficiency and data throughput. We analyze the performance of each frame aggregation scheme in distinct scenarios, and we conclude that overall, the two-level aggregation is the most efficacious