A personal wireless area network (WPAN) is a network used for communication among computing devices (for example, telephones and personal digital assistants) close to one person. The devices may or may not belong to the person in question. The reach of a WPAN may be a few meters. WPANs may be used for intrapersonal communication among the personal devices themselves, or for connecting via an uplink to a higher level network and the Internet. Personal area networks may be wired with computer buses such as a universal serial bus (USB) and FireWire.
The IEEE 802.15.3 Task Group 3c (TG3c) was formed in March 2005. TG3c is developing a millimeter-wave (mmWave) based alternative physical layer (PHY) for the existing 802.15.3 Wireless Personal Area Network (WPAN) Standard 802.15.3-2003. This mmWave WPAN may operate in a frequency band such as the 57-64 GHz unlicensed band defined by FCC 47 CFR 15.255. The millimeter-wave WPAN may allow high coexistence, in a close physical spacing, with all other microwave systems in the 802.15 family of WPANs. In addition, the millimeter-wave WPAN may allow a very high data rate of over 2 Gigabit per second (Gbps) for applications such as high speed internet access, streaming content download (e.g., video on demand, high-definition television (HDTV), home theater, etc.), real time streaming and wireless data bus for cable replacement. Optional data rates in excess of 3 Gbps may be provided.
In addition to the 802.15.3c Task Group, the IEEE 802.11 Working Group is also forming a Task Group to define a wireless local area network (WLAN) also operating in the millimeter-wave frequencies.
However, a mmWave communication link is significantly less robust than those at lower frequencies (e.g. 2.4 GHz and 5 GHz bands) due to both oxygen absorption and high attenuation through obstructions. In addition, the mmWave communication link may use directional antenna to increase the communication range, but the use of directional antenna makes a link very sensitive to mobility. For example, a slight change in the orientation of the device or the movement of a nearby object and/or person may disrupt the link.
In order to satisfy a link budget requirement, two forms of communication may be used. The first form is an Omni mode and the second form is a directional mode. In the Omni mode a low rate transmission (e.g., in the order of a few Megabit per second (Mbps)) and/or multiple directional transmissions (emulating an omni coverage) may be employed to compensate for the loss of antenna gain due to the (quasi) omni transmission. In the directional mode a high rate transmission (e.g., in the order of Gbps) may be used since the link employs directional antennas and hence may benefit from the higher antenna gain.
In the Directional mode various access schemes may be used. For example, a Carrier-Sense Multiple Access with Collision Avoidance (CSMA/CA) may be used at 60 GHz when high-data rate directional communication is desired and Time division Multiple Access (TDMA) access if desired. However, one of the deficiencies of TDMA is that it has very high scheduling latencies (e.g., at least one superframe worth of latency) which is unacceptable for applications requiring low latency such as Internet traffic and Wireless I/O. Furthermore, the TDMA access scheme in Directional mode may not allow a dynamical de-allocation and reallocation of a channel bandwidth. With regards to CSMA/CA, its performance at 60 GHz may not be desirable since it requires the use of low rate omni direction transmission. Thus there is a need for an access scheme that allows bandwidth to be de-allocated and reallocated dynamically based on traffic demands.
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