Getting the most of WiFi mesh networks with 802.16 mesh emulation

Abstract

Currently deployed wireless mesh networks are based on 802.11, WiFi technology, which is not efficient in multihop scenarios. We present a method, which emulates 802.16 mesh networks over 802.11 hardware. The method works by embedding 802.16 packets into 802.11 broadcast packets and padding the 802.11 broadcast payload, so that the broadcasts are aligned to 802.16 time division multiple access frame boundaries. The method requires only software changes on the nodes using 802.11a for mesh communications. This means that the mesh networks installed with 802.11a hardware today can be upgraded with a software patch to take advantage of quality-of-service available in 802.16.

We use ns2 simulations to show the performance of the 802.11 based mesh networks with the embedded 802.16. We show that the hybrid system can achieve throughputs in multiples of what is possible with 802.11 hardware alone. First, the efficiency of the new system is significantly higher than the efficiency of 802.11 based systems, because we use broadcast packets. Second, the new system eliminates unnecessary collisions in the wireless channel since it takes advantage of scheduled wireless access with 802.16 mesh coordination function.

Keywords:

• time division multiple access
• 802.11 real-time scheduling
• distributed coordination function
• mesh coordination function
• MAC

Notes

^1. Currently at University of California, Davis, One Shields Ave., Davis, CA, USA.

^2. This work was carried out while the first author was a Ph.D. candidate at the University of Toronto.

^3. This work was sponsored in part by the LG Electronics Corporation.

^4. IEEE 802.16 can use hardware with 10 MHz, in the licensed 5 GHz frequency band, or 20 MHz, in the license-exempt 5 GHz frequency band, while 802.11a uses 20 MHz in the license-exempt 5 GHz frequency band.

^5. The standard restricts the number of transmission opportunities in the data sub-frame to at most 256 because the duration fields in the scheduling control packets are 8 bits long.

^6. It is possible to embed the packets in conjution with the sub-network access protocol (SNAP) [9]. However, this is not necessary under Linux because the kernel allows the definition of custom ethernet types, so we opted to use an embedding with a smaller size, i.e. without the SNAP sub-header.

^7. For real implementations, this assumption depends on the firmware support. For example, the Intel PRO/Wireless 2900bg cards allow this change (Intel^® PRO/Wireless 2200BG driver for linux, http://ipw2200.sourceforge.net/).

Additional information

Notes on contributors

Petar Djukic

1. 1. Currently at University of California, Davis, One Shields Ave., Davis, CA, USA.

Shahrokh Valaee

2. 2. This work was carried out while the first author was a Ph.D. candidate at the University of Toronto. 3 3. This work was sponsored in part by the LG Electronics Corporation.