Integrating multiuser dynamic OFDMA into IEEE 802.11a and prototyping it on a real-time software-defined radio testbed

Abstract

Multiuser dynamic orthogonal frequency division multiple access (OFDMA) can achieve high downlink capacities in future wireless networks by optimizing the subcarrier allocation for each user.When it comes to the integration into current wireless local area network (WLAN) standards, dynamic OFDMA raises several implementation issueswhich are neglected in theoretical papers. Putting this emerging approach into practice requires to treat these issues accordingly and to demonstrate the feasibility of the system design. In this paper, we propose a dynamic OFDMA integration for the physical layer of the widespread IEEE 802.11a standard. To test our implementation and demonstrate its practical relevance we use a pragmatic approach: We prototype multiuser dynamic OFDMA on a real-time software-defined radio testbed for WLANs. We discuss details of our implementation and provide measurements showing that it does not introduce significant overhead into the IEEE 802.11a system at high subcarrier allocation quality. We particularly focus on the problems of our integration as well as the concepts and limitations of the used testbed.

Integrating Multiuser Dynamic OFDMA into IEEE 802.11 WLANs - LLC/MAC Extensions and System Performance

“…On the downlink these data frames are transmitted using either dynamic OFDMA or standard IEEE 802.11a OFDM-TDD. With dynamic OFDMA, the dynamic OFDMA-extended IEEE 802.11a PHY described in [13] is used where each WT receives a subset of S j = S/J different subcarriers. In this PHY, rate adaptation is performed as above except that channel state is measured and PHY rate is adapted per subcarrier.…”

“…Here, further training sequences and pilots would improve adaptation accuracy but increase training overhead. Nonetheless, measurements have shown that in typical indoor and urban WLAN scenarios with low and medium mobility our above PLCP-based method suffices [13]. Using this method, the chosen PHY rate leads to either 0.5, 0.75, 1, 1.5, 2, 3, 4 or 4.5 uncoded data bits per subcarrier.…”

“…The chosen number of bits per subcarrier is passed to the ebDA subcarrier allocation algorithm [13], i.e. a runtimeoptimized version of the basic Dynamic Algorithm (bDA) [9].…”

“…even considering bit-and power allocation, may reach better performance. However, experiments on WLAN PHY prototypes have shown that its small and predictable runtime makes ebDA feasible for implementation [13]. Nevertheless, improved allocation algorithms can be easily integrated in our system.…”

“…We study the application layer performance of this system and analyze the effects of our MAC/LLC extensions. For this study, we exemplarily combine our extensions with a simple subcarrier allocation heuristic and an IEEE 802.11a OFDMA PHY [13]. Nonetheless, other heuristics, e.g.…”