The XPress Ethernet Bridge (XEB) is well-suited for video applications that require longer range distance (1000ft non-line of sight) using medium or low video resolution and medium or low frame rates (frames per second). For video applications with high resolution or a high frame rates we encourage a faster protocol such as 802.11g, although the range will be much less (300ft non-line of sight). In a few applications where only low resolution and low frame rates are required, Digi serial radios (XCite, XStream, XTend, XBee) can be used.
Generally it is wise to choose a radio that provides a little higher bandwidth than is actually needed. This will allow for reduced bandwidth in real-life, imperfect conditions. Conditions that decrease effective bandwidth include physical obstructions, interference, and RF protocol overhead. Bandwidth is decreased due to numerous retransmissions, thus reducing the total possible number of frames per second. Since true video transmission requires high bandwidth (20-30 frames per second), data compression is required. Please consider the following reference table comparing the expected bandwidth in Frames per second (Fps) for a camera using MPEG-2 compression:Expected Bandwidth*
*Assuming 24 bits/pixel and 40:1 (MPEG-2) compression ratio. Lower color quality could be used(e.g. 8 bits/pixel) to increase Bandwidth.
35 Mbps (802.11g)||
935 Kbps (XPress)||
115 Kbps (XTend)|
160 x 120||
320 x 240||
640 x 480||
160 x 120 -> 11.5Kbp/F
320 x 240 -> 46.1Kbp/F
640 x 480 -> 184.3Kbp/FPlease note that some systems may be limited by the particular video camera's specifications. For Example:
We tested the eCAMit III camera by 3JTech, which sends a maximum of 15 Fps @ 320 x 240 resolution or 6 Fps @ 640 x 480. Suppose you are trying to decide whether to use the XPress radio or an 802.11g radio for 320 x 240 resolution. According to the table above the XPress radio can send 20Fps and the 802.11g radio can send 760Fps. Since the eCAMit III camera has a maximum Frame rate of 15 Fps, the XPress radio and 802.11g radio will yield the same results: 15 Fps.