User's Manual

U-NII Config & User Guide 5.2 Axxcelera Broadband Wireless
energy that is ‘leaked’ into surrounding areas, which appears as interference. In FDD
systems, it is quite difficult to accurately control the channel’s power since a feedback
path is required. No such path is needed in a TDD system since the same channel is
used in both directions. The SU needs to only measure the received power from the
AP in order to know how much to attenuate its upstream transmission.
• Channel Efficiency – Because each frame carries upstream and downstream traffic
in proportion to the offered load in each direction, adaptive TDD systems are highly
efficient in its use of bandwidth. FDD systems have to make an estimate of the traffic
mixture and allocate channel bandwidth accordingly. As shown in the chart below,
any variation from this estimate (in this case 15:1 downlink) will result in wasted
bandwidth. This variation is inevitable due to the diurnal variation of business usage
during the daytime hours, residential usage in the afternoon and evening, a varying
mixture of user types according to the geographic location, and an ever-changing set
of user applications.
13.8 AP and SU Specifications
13.8.1 AP/SU/Extender Functional Block Diagram
The Access Point and Subscriber Unit functional block diagram is shown below. The
analog radio portion is highlighted in blue, while the digital section containing the
modem is in yellow.
March 10, 2003 Company Confidential Page 133 of 149