Ad-hoc networks include multiple devices or nodes that exchange wireless signals. During operation, nodes may enter and leave the proximity of other nodes. Thus, the composition of an ad-hoc network may change over time. Moreover, the mobility of nodes may cause changes in various network characteristics, such as topology. Despite a lack of centralized authority or existing infrastructure, ad-hoc networks are typically capable of rearranging themselves in response to such events.
Recently, ad hoc networking techniques have been considered an attractive technology for implementing mesh networks, which provide a multipoint-to-multipoint network topology. In such networks, communication between two devices may occur across one or more intermediate or relaying nodes. Such communications are referred to as multihop communications.
The application of ad-hoc communications techniques to multihop networking is viewed as a way to provide new applications for mobile device users. In addition, this application has the potential to provide new opportunities for the communications industry in the areas of terminal manufacturing, software engineering, and the deployment of network infrastructure to interconnect ad-hoc networks. Moreover, this application of ad-hoc communications techniques to multihop networking provides for various consumer uses. Examples of such uses include applications related to teenager and other group networking, Internet access, authentication applications, and home networking.
Bluetooth and wireless local area networks (WLAN) are examples of wireless ad-hoc networking technologies. Bluetooth provides a short-range radio network, originally intended as a cable replacement. It can be used to create ad hoc networks of up to eight devices, where one device is referred to as a master device. The other devices are referred to as slave devices. The slave devices can communicate with the master device and with each other via the master device. The devices operate in the 2.4 GHz radio band reserved for general use by Industrial, Scientific, and Medical (ISM) applications. Bluetooth devices are designed to find other Bluetooth devices within their communications range and to discover what services they offer.
WLANs are local area networks that employ high-frequency radio waves rather than wires to exchange information between devices. IEEE 802.11 refers to a family of WLAN standards developed by the IEEE. In general, WLANs in the IEEE 802.11 family provide for 1 or 2 Mbps transmission in the 2.4 GHz band using either frequency hopping spread spectrum (FHSS) or direct sequence spread spectrum (DSSS) transmission techniques.
Within the IEEE 802.11 family are the IEEE 802.11b and IEEE 802.11g standards. IEEE 802.11b (also referred to as 802.11 High Rate or Wi-Fi) is an extension to IEEE 802.11 and provides for data rates of up to 11 Mbps in the 2.4 GHz band. This provides for wireless functionality that is comparable to Ethernet. IEEE 802.11b employs DSSS transmission techniques. IEEE 802.11g provides for data rates of up to 54 Mbps in the 2.4 GHz band. For transmitting data at rates above 20 Mbps, IEEE 802.11g employs Orthogonal Frequency Division Multiplexing (OFDM) transmission techniques. However, for transmitting information at rates below 20 Mbps, IEEE 802.11g employs DSSS transmission techniques. The DSSS transmission techniques of IEEE 802.11b and IEEE 802.11g involve signals that are contained within a 23 MHz wide channel. Several of these 23 MHz channels are within the ISM band.
Other technologies are also applicable for the exchange of information at higher data rates. Ultra wideband (UWB) is an example of such a higher data rate technology. Since gaining approval by the Federal Communications Commission (FCC) in 2002, UWB techniques have become an attractive solution for short-range wireless communications. Current FCC regulations permit UWB transmissions for communications purposes in the frequency band between 3.1 and 10.6 GHz. However, for such transmissions, the spectral density has to be under −41.3 dBm/MHz and the utilized bandwidth has to be higher than 500 MHz.
There are many UWB transmission techniques that can fulfill these requirements. A common and practical UWB technique is called impulse radio (IR). In IR, data is transmitted by employing short baseband pulses that are separated in time by gaps. Thus, IR does not use a carrier signal. These gaps make IR much more immune to multipath propagation problems than conventional continuous wave radios. RF gating is a particular type of IR in which the impulse is a gated RF pulse. This gated pulse is a sine wave masked in the time domain with a certain pulse shape.
To participate in an ad-hoc multihop network, a device needs to provide several features. Examples of such features include interference avoidance, link management, and routing. Moreover, certain wireless communication technologies are better suited for the exchange of control information, while other wireless communication technologies may be better suited for the transfer of user data. For instance, Bluetooth on its own is not well suited for many forms of user data. However, higher data rate technologies (e.g., WLAN and UWB) are often not efficient for the transfer of network control information.
Therefore, techniques are needed for the effective use of ad hoc techniques. in multihop networks.