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

ARK: automatic retransmission queuing

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 US)

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

CoS: class of service

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 Canada (Canadian peer to FCC)

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 Watts. It can also be expressed in dBm. The relation between dBm and Watts can be expressed as follows: PdBm = 10 x Log Pmw For example: 1 Watt = 1000 mW; PdBm = 10 x Log 1000 = 30 dBm 100 mW; PdBm = 10 x Log 100 = 20 dBm For link budget calculations, the dBm convention is more convenient than the Watts convention.

 

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 = 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.