Practical applications include radiolinks in offices and factory buildings, production and laboratory floors covering one or multiple stories. Connectivity may also wish to be extended campus-wide. Here we mean that communication may also be desired over and around several buildings and adjacent properties. IEEE 802.16 documentation gives the maximum bit rate supported as 155 Mbps. Let us assume a receiver noise figure of 5 dB and transmitter output power of 2.0 W or +6 dBW, transmission line losses of 3 dB and an antenna gain of 0 dBi, what kind of performance can we expect on an LOS path 1 km distant? The model link is set out in a tabular form beginning with the transmitter power output placed at the top of the column. The abbreviation RSL means the "receive signal level." This term is widely used on RF systems. RSL is conventionally measured in dBW or dBm.
We also establish a performance requirement expressed as BER at 1X10 -10. where the E b/N o = 17 dB including 2 dB of modulation implementation loss.
E b/N o is energy per bit (E b) per noise density ratio (N o). In our table below E b = RSL divided by the bit rate. N o = thermal noise in 1 Hz of bandwidth and is calculated as –204 dBW + 10Log(noise figure). The noise figure of the model receiver is 5 dB, then N o = -204 dBW + 5 dB = -199 dBW/Hz.
Model outdoor-indoor link power budget
|Transmitter power output||+6 dBW||4 W equiv.|
|Trans line losses||-3 dB||Approx|
|Trans ant gain||0 dBi||
|LOS free space loss at 1 km, @ 2.5, 5.2 GHz|| -100.36 dB (2.5 GHz)
-106.72 dB (5.2 GHz)
|Rec ant gain||0 dBi||
|Miscl line losses||-3 dB||
|Rec signal level (RSL)||-97.36 dBWemail@example.com GHz|
|Rec signal level (RSL)||-103.72 dBWfirstname.lastname@example.org GHz|
|Link bit rate||155x106 bps||81.9 dB equiv|
| Eb, (RSL = -106.36 dBW)
Eb (RSL = -112.72 dBW)
| -179.26 dBW
| @2.5 GHz
|Eb/No|| 19.74 dB (2.5 GHz)
13.38 dB (5.2 GHz)
|No= -199 dBW/Hz|
|No = -199 dBW/Hz|
FSL = 32.4 + 20Log2500 = 32.4 + 67.96 = 100.36 dB at 1 km, 2.5 GHz
32.4 + 20log5200 = 106.72 dB at 1 km, 5.2 GHz
About the author:
Roger Freeman has worked in telecommunications since 1946 when he joined the Navy and became an aviation radioman. Later, Roger served as a radio officer in the merchant marine for nearly 10 years. He then held several positions with ITT assigned to their Spanish Standard Electrica subsidiary. He also served the International Telecommunication Union as Regional Planning Expert for Northern Latin America based in Quito, Ecuador. Roger is bilingual. His last employee position was principal engineer with the Raytheon Company, Marlboro, MA where he took early retirement in 1991 to establish Roger Freeman Associates, Independent Consultants in Telecommunications. He has been giving seminars in telecommunication disciplines at the University of Wisconsin, Madison for nearly 20 years. Roger has been writing books on various telecommunication subjects for John Wiley & Sons since 1973. There are seven titles which he keeps current including the two-volume work, Reference Manual for Telecommunication Engineers, now in 3rd edition. He holds two degrees from NYU. His Web site is www.rogerfreeman.com and his e-mail address is email@example.com.