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Common abbreviations and/or acronyms... 477: (Form
477) FCC's mandatory broadband reporting form for commercial operators AAA server:
authentication authorization accounting server APD:
automatic protocol detection AES OCB:
usually just called "AES," advanced encryption standard offset codebook AIFS:
arbitration inter-frame spacing AP: access
point ARS:
automatic rate switching ASN-GW:
access service network gateway ATPC:
automatic transmit power control AU: access
unit (same as above) BE: best
effort BER: bit
error rate BRS:
Broadband Radio Service (commercial side of the 2.5 GHz allocation in the BSS: basic
service set BST: base
station (referred more often this way in licensed networks) BWA:
broadband wireless access BWIA:
broadband wireless Internet access (Steve Stroh's preferred acronym) CBR:
constant bit rate CC: convolutional coding CDL: cell
distance learning (refers to an automatic process within RF devices) CDMA: code
division multiple access CG (or
UGS): constant grant or unsolicited grant service CIR:
committed information rate CPE:
customer premises equipment C/I:
carrier to interference ratio CSMA/CA:
carrier sense multiple access/collision avoidance EBS:
Educational Broadband Spectrum (2.5 GHz allocated to non-profits, may be
sublet), formerly ITFS (Instructional Fixed Television Service) DFS:
dynamic frequency selection DFS2 or
DFS+: second generation DFS (mandated for all new 5.3 and all 5.4 GHz) DIFS:
distributed coordination function inter-frame spacing) DS (or
DSSS): direct sequence spread spectrum EIRP:
effective isotropic radiated power (expressed in dB) EMI:
electromagnetic interference ESSID:
extended service set ID FCC:
Federal Communications Commission FDD:
frequency division duplex FEQ:
forward error correction FFT: fast fourier transform mathematical
algorithm FH (or
FHSS): frequency hopping spread spectrum FIPS:
federal information processing standards GFSK: Gaussian
frequency shift keying HIPPA:
Healthcare Insurance Portability and Accountability Act IC:
Industry IDU: indoor
unit IF: intermediate
frequency ISM:
Industrial, Scientific, and Medical LOS: Line
of sight LQI: link
quality indicator MAC: media
access control MAN:
metropolitan area network MIB:
management information bit(s) MIR:
maximum information rate NLOS:
Near/non LOS NMS:
network management system NPU:
network processing unit OA&M:
operation, administration & maintenance ODU:
outdoor unit OET: Office
of Engineering and Technology (FCC division responsible for equipment
authorization and rules enforcement) OFDM:
orthogonal frequency division multiplexing OFDMA:
orthogonal frequency division multiple access OBE or
OOBE: out-of-band emissions PAN:
personal area network Part 15:
refers to FCC regulations in Part 15.247 of the Federal Code governing certain
UL bands PIU: power
interface unit PoE:
power over Ethernet PtMP or PmP: point-to-multipoint PtP:
Point-to-point QAM: quadrature amplitude modulation QinQ:
VLAN type that allows customer to have own VLAN inside the operator's VLAN QoS:
quality of service; the idea that network transmission rates, error rates, and other characteristics can be measured, improved, and to some extent, guaranteed in advance using different techniques and strategies that are designed to ensure predictable service from the network and its associated components RAN: radio
access network RFI: radio
frequency interference RSSI:
receive(r) signal strength index/indication rtPS: real time polling services RTS/CTS:
request to send, clear to send Rx: receive RTCP: real
time control protocol RTP: real
time protocol SCADA:
supervisory control and data acquisition SDR:
software defined radio SIF: short
inter-frame spacing SIP:
session initiation protocol SNR: signal
to noise ratio SOFDMA:
scalable orthogonal frequency division multiple access STC: space
time coding TDD: time
division duplex TDMA: time
division multiple access TVoIP: TV
over IP Tx: transmit UL: offen used to abbreviate "unlicensed," but also
could mean "uplink" UNII:
Unlicensed-National Information Infrastructure VLAN:
virtual LAN VoIP:
voice over IP VPN:
virtual private network VOFDM:
vector OFDM WCS:
Wireless Communications Service (2.3 GHz licensed band) WEP: wired
equivalent privacy WiMAX:
wireless interoperability, microwave access WLAN:
wireless LAN WLL:
wireless local loop Some
terms... dB: The dB convention is an abbreviation for
decibels. It is a mathematical expression showing the relationship between two
values. RF Power
Level: RF power level at either
transmitter output or receiver input is expressed in Attenuation: Loss of power, expressed in dB Attenuation is
expressed in dB as follows: PdB = 10 x Log (Pout/Pin)
For example: If, due to attenuation, half the power is
lost (Pout/Pin = 2), attenuation in dB is 10 x Log (2) = 3dB Path Loss: Path loss is the loss of power of an RF
signal traveling (propagating) through space. It is expressed in dB. Path loss
depends on: 1. The
distance between transmitting and receiving antennas. 2. Line of
sight clearance between the receiving and transmitting antennas. 3. Antenna
height. Free Space
Loss: Attenuation of the electromagnetic wave while propagating through space. This
attenuation is calculated using the following formula: Free space loss = 32.4 +
20xLog F(MHz) + 20xLog R(Km) F is the RF frequency expressed in MHz. R is the
distance between the transmitting and receiving antennas. At 2.4 Ghz, this formula is: 100+20xLog R(Km) Isotropic
Antenna: A hypothetical, lossless
antenna having equal radiation intensity in all directions. Used as a zero dB gain
reference in directivity calculation (gain). The sun is often given as an
example of an isotropic radiator. Gain: Antenna gain is a measure of directivity. It
is defined as the ratio of the radiation intensity in a given direction to the
radiation intensity that would be obtained if the power accepted by the antenna
was radiated equally in all directions (isotropically).
Antenna gain is expressed in dBi. Radiation
Pattern: The radiation pattern is a
graphical representation in either polar or rectangular coordinates of the spatial
energy distribution of an antenna. Side Lobes: The radiation lobes in any direction other
than that of the main lobe. Omni-directional
Antenna: This antenna radiates and
receives equally in all directions in azimuth. Directional
Antenna: This antenna radiates and
receives most of the signal power in one direction. Antenna Beamwidth: The directiveness of a directional antenna. Defined as the
angle between two half-power (-3 dB) points on either side of the main lobe of
radiation. Receiver
Sensitivity: The minimum RF signal power
level required at the input of a receiver for certain performance (e.g. BER). EIRP
(Effective Isotropic Radiated Power): The antenna transmitted power equal to
the transmitted output power minus cable loss plus the transmitting antenna
gain. EIRP = Pout - Ct + Gt Pout = Output power of
transmitted in dBm Ct = Transmitter cable attenuation
in dB Gt = Transmitting antenna gain in dBi Gr = Receiving antenna gain
in dBi Pl = Path loss in dB Cr = Receiver cable
attenuation is dB Si = Received power level at
receiver input in dBm Ps = Receiver sensitivity is dBm Si = Pout - Ct + Gt - Pl + Gr - Cr Example: Link
Parameters: Frequency: 2.4 Ghz Pout = 4 dBm (2.5 mW) Tx
and Rx cable length (Ct and Cr) = 10 m. cable type RG214 (0.6 dB/meter) Tx and Rx antenna gain (Gt and Gr) = 18 dBi Distance between
sites = 3 Km Receiver sensitivity (Ps) = -84 dBm. Link Budget Calculation EIRP = Pout - Ct + Gt = 16 dBm Pl = 32.4 + 20xLog F(MHz) + 20xLog R(Km) @ 110 dB Si
= EIRP - Pl + Gr - Cr = -82 dBm
In conclusion, the received signal power is above the sensitivity threshold, so
the link should work. The problem is that there is only a 2 dB difference
between received signal power and sensitivity. Normally, a higher margin is
desirable due to fluctuation in received power as a result of signal fading. Pout =
Output power of transmitted in dBm Ct =
Transmitter cable attenuation in dB Gt =
Transmitting antenna gain in dBi Gr =
Receiving antenna gain in dBi Pl = Path
loss in dB Cr =
Receiver cable attenuation is dB Si =
Received power level at receiver input in dBm Ps =
Receiver sensitivity is dBm Si = Pout
- Ct + Gt - Pl + Gr - Cr Example: Link
Parameters: Frequency:
2.4 Ghz Pout = 4 dBm (2.5 mW) Tx and Rx cable length (Ct and Cr) = 10 m. cable type RG214
(0.6 dB/meter) Tx and Rx antenna gain (Gt and Gr) = 18 dBi Distance
between sites = 3 Km Receiver
sensitivity (Ps) = -84 dBm Link Budget
Calculation EIRP = Pout
- Ct + Gt = 16 dBm Pl = 32.4 +
20xLog F(MHz) + 20xLog R(Km) @ 110 dB Si = EIRP
- Pl + Gr - Cr = -82 dBm In
conclusion, the received signal power is above the sensitivity threshold, so
the link should work. The problem is that there is only a 2 dB difference
between received signal power and sensitivity. Normally, a higher margin is
desirable due to fluctuation in received power as a result of signal fading. Signal
Fading: Fading of the RF signal is
caused by several factors: 1. Multipath The
transmitted signal arrives at the receiver from different directions, with
different path lengths, attenuation and delays. The summed signal at the
receiver may result in an attenuated signal. 2. Bad Line
of Sight An optical
line of sight exists if an imaginary straight line can connect the antennas on
either side of the link. Radio wave clear line of sight exists if a certain
area around the optical line of sight (Fresnel zone) is clear of obstacles. A
bad line of sight exists if the first Fresnel zone is obscured. 3. Link
Budget Calculations 4. Weather
conditions (Rain, wind, etc.) At high rain intensity (150 mm/hr), the fading of
an RF signal at 2.4 Ghz may
reach a maximum of 0.02 dB/Km. Wind may cause fading due to antenna motion. 5.
Interference Interference
may be caused by another system on the same frequency range, external noise, or
some other co-located system. The Line of
Sight Concept: An optical line of sight
exists if an imaginary straight line can be drawn connecting the antennas on either
side of the link. Clear Line
of Sight: A clear line of sight exists
when no physical objects obstruct viewing one antenna from the location of the
other antenna. A radio wave clear line of sight exists if a defined area around
the optical line of sight (Fresnel Zone)is clear of
obstacles. Fresnel
Zone (pronounced: fruh nell): The
Fresnel zone is the area of a circle around the line of sight. The Fresnel Zone
is defined as follows: R1 = ½ square root of (lxD) R:
radius of the first Fresnel zone l: wavelength D: distance between sites Fairness
Factor: The Fairness Factor enables to
define the level of fairness in providing services to different SUs. When set
to 100%, all SUs have the same probability of getting services when competing
for bandwidth. If set to X%, then SUs located up to X% of the maximum distance
from the AU will have an advantage in getting services over SUs located farther
than this distance. |