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
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
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
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
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
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
dB: The dB convention is an abbreviation for decibels. It is a mathematical expression showing the relationship between two values.
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
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:
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.
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.