Dynamic Band Selection Technique for Dual-band Wireless LAN System

1. INTRODUCTION With the enormous growth of computer-based terminals, the demands for indoor network which enable us to transmit and share digital information have been rapidly increased. As a method to form indoor office/home network, wireless LAN (WLAN) systems have taking a great attention, as they provides attractive features such as an ease of network constructions, a flexibility of network reconfigurations, and so on. Among several kinds of WLAN systems, a 2.4GHz-band WLAN system based on IEEE802.11g standard [1] and a 5GHz-band WLAN system based on IEEE802.11a standard [2] attract international attention. However, since the radio frequency bands used to transmit data packets differ, 2.4GHz-band and 5GHz-band WLAN systems cannot communicate each other, and also have quite different characteristics in their performances. For example, 2.4GHz radio frequency band is originally prepared for Industrial, Scientific and Medical (ISM) apparatus such as microwave ovens, and the performance of 2.4GHz-band WLAN system is much degraded by the effect of man-made noise with the coexistence of ISM apparatus. On the contrary, in 5GHz-band WLAN system, because of using the relative high radio frequency band, the effect of both propagation loss and shadowing in 5GHz-band WLAN system becomes large compared with those in 2.4GHz-band WLAN system. As one of the methods to solve the problem about mutually connection between 2.4GHz-band and 5GHz-band WLAN systems, a combo chip compatible with IEEE802.11a/b/g standards is developed and already put in practical use. Access point (AP) or terminals having the combo chip are able to communicate without caring the standards of the other side, and it is expected that the WLAN system corresponding to the dual-band (hereafter, it is called a dual-band WLAN system) spreads widely. However, in conventional dual-band WLAN system, a radio frequency band employed in wireless communication is assigned to a terminal when connecting with network and the terminal only uses this radio frequency band until the terminal disconnects from the network. In this paper, we propose a dynamic band selection technique for dual-band WLAN systems. In the proposed technique, a radio frequency band employed for the transmission of data packet is changed on packet-by-packet basis according to the channel conditions of 2.4GHz and 5GHz radio frequency band, and then a high throughput performance can be expected by using proposed technique.