2 WipLL Radio Technology Physical Layer The WipLL system provides wireless, local-loop connectivity between the provider’s IP-based backbone and the subscriber. This radio link is established between WipLL transceivers located at the Base Station and subscriber sites.
WipLL Radio Technology - Physical Layer System Description 2.1. Frequency Hopping Spread Spectrum The WipLL system implements frequency-hopping code division multiple access (FH-CDMA) spread spectrum modulation for digital signal transmission over the air between the Base Station and the subscriber site. The WipLL system’s frequency hopping supports a channel bandwidth of 1 MHz or 1.33 MHz, and channel spacing of 1 MHz (or 1.75 MHz if operating in the 3.5 GHz band).
System Description WipLL Radio Technology - Physical Layer The advantages of implementing FH-CDMA in the WipLL system include the following: Frequency Hopping Spread Spectrum (FHSS) is based on interference avoidance. Narrow band interference that does not meet the SNR blocks only a few hops, decreasing the throughput only partially. The required spectrum for an FHSS system is flexible in that it does not have to be contiguous. FHSS can coexist with other systems in the same spectrum band.
WipLL Radio Technology - Physical Layer System Description Table 2-1 shows an example of six orthogonal sequences that can be derived from seven sub-channels. Table 2-1: Example of six orthogonal FH sequences Sequence No. Sub-channels (frequencies) 1 0 1 2 3 4 5 6 2 0 2 4 6 1 3 5 3 0 3 6 2 5 1 4 4 0 4 1 5 2 6 3 5 0 5 3 1 6 4 2 6 0 6 5 4 3 2 1 Up to 32 such sequences, each with up to 99 sub-channels can be pre-configured in the WipLL ROM.
System Description WipLL Radio Technology - Physical Layer FSK provides the following benefits: Non-coherent detection is possible - no carrier synchronization is required. Immunities to non-linearity - the envelope contains no information and, therefore, can be hard-limited; information is carried by zero crossings: Can be used with non-linear power amplifiers Better efficiency The FSK phase can be discontinuous or continuous, as displayed in Figure 2-4.
WipLL Radio Technology - Physical Layer System Description 2.3. Frequency Bands WipLL provides a Wireless Local Loop (WLL) solution in the following frequency bands: Licensed bands: 700 MHz (698 – 746 MHz) 2.5 GHz (MMDS) 2.8 GHz (TDD) 3.3 to 3.8 GHz TDD/FDD (50 or 100 MHz duplex separation) Unlicensed bands: ISM 900 MHz (902 MHz to 928 MHz) ISM 2.4 GHz (TDD) 5.8 GHz (TDD) For details on specific WipLL products, see Appendix B. 2-6 Airspan Networks Inc.
System Description WipLL Radio Technology - Physical Layer 2.4. Standards Compliance Table 2-2 lists standards to which WipLL complies. Table 2-2: WipLL standards compliance Standard EMC Compliance • 700 MHz: FCC part 27 • 900 MHz: FCC part 15 • 2.4 GHz: ETS 300 826; FCC part 15 • MMDS: FCC part 21 • 3.5 GHz: EN 300 385; EN 300 386-2; ETS 300 132-2 • 5.8 GHz: FCC part 15 Radio • 700 MHz: FCC part 27 • 900 MHz: FCC part 15 • 2.4 GHz: EN 300 328-1; FCC part 15; RSS 139; Telec • MMDS: FCC part 21 • 3.
WipLL Radio Technology - Physical Layer System Description 2.5. WipLL RF Antennas WipLL provides a variety of internal antenna types as well as an option for connecting off-the-shelf, third-party external antennas. Table 2-3 provides a general description of the WipLL RF antenna parameters. Table 2-3: WipLL RF antenna specification Parameter Description • Integral flat-printed antenna: for BSR, PPR, SPR, and IDR devices: No RF cable is involved for connection between BSR and SPR.
System Description WipLL Radio Technology - Physical Layer 2.5.1. WipLL Internal Antenna Specifications Table 2-4, Table 2-5, Table 2-6, and Table 2-7 list the internal antenna specifications of the BSR, PPR, SPR, and IDR devices, respectively. Table 2-4: BSR (Base Station) antenna specifications Parameter Frequency Gain range (dBi) (MHz) Beam Polarization VSWR Impedance Frontwidth to(ohm) HXV back ratio (degrees) (dB) 900 MHz 902 - 928 8 60 x 60 Vertical 1:1.5 50 25 2.
WipLL Radio Technology - Physical Layer System Description Table 2-6: SPR (CPE – outdoor unit) antenna specifications SPR Type Freq. range (MHz) Gain (dBi) Beam width HXV (deg. Polarization VSWR Impedance (ohm) Front -toback ratio (dB) 700 MHz 710 - 716 & 740- 746 8 60 x 60 Vertical 1:1.6 50 20 900 MHz 902 - 928 8 60 x 60 Vertical 1:1.9 50 23 2.4 GHz 2,400 2,500 15 24 x 33 Vertical 1:1.6 50 28 High-gain 2.4 GHz 2,400 2,500 18 19 x 25 Vertical 1:1.
System Description WipLL Radio Technology - Physical Layer Table 2-7: IDR (CPE - indoor unit) antenna specifications IDR Type Freq. range (MHz) Gain (dBi) Beam width HXV (deg.) Polarization VSWR Impedance Frontto(ohm) back ratio (dB) 900 MHz 902 - 928 8 67 x 93 Vertical 1:1.9 50 -17 2.4 GHz 2,400 to 2,500 10 65 x 32 Vertical 1:1.6 50 25 3.5 GHz 3,400 to 3,600 10 65 x 32 Vertical 1:1.6 50 25 2.5.2.
WipLL Radio Technology - Physical Layer System Description 2.5.2.2. Sector Antenna This antenna is designed for best non-line of sight performance with Airspan’s BSR operating in the 900 MHz band. Advanced features include: high gain and mechanical downtilt. Electrical specifications Frequency range 870 –960 MHz Polarization Vertical Gain 15.5 dBi Half-power beam width • H-plane:65° • E-plane:13° Front-to-back ratio >25 dB Impedance 50 . VSWR <1.
System Description WipLL Radio Technology - Physical Layer Weight 6 kg Wind load • Frontal: 220 N (at 150 km/h) • Lateral: 140 N (at 150 km/h) • Rearside: 490 N (at 150 km/h) Max.wind velocity 200 km/h Packing size 1422 x 272 x 160 mm Height/width/depth 1294 /258 /103 mm 2.5.2.2.1. Omnidirectional Antenna This antenna is designed for best non-line of sight performance with Airspan’s BSR operating in the 900 MHz band.
WipLL Radio Technology - Physical Layer System Description Mechanical specifications Model Type 736 347 736 348 Input 7-16 female 7-16 female Connector position Bottom Top Weight 8 kg Radome diameter 51 mm Wind load 210 N (at 150 km/h) Max.wind velocity 200 km/h Packing size 3316 x 148 x 112 mm Height/width/depth 3033 mm 3022 mm 2.5.2.3.
System Description WipLL Radio Technology - Physical Layer 2.5.2.3.1. 10 dBi Panel Electrical Frequency range 902 - 928 MHz Gain 10 dBi (min) VSWR 1.
WipLL Radio Technology - Physical Layer System Description Solar radiation ASTM G53 1000 h - - Flammability UL 94 - - CLASS HB Salt spray IEC 68-2-11 Ka 500 h - - Ice and snow - - - 25mm radial Wind speed survival - - - 220 Km/h 160 Km/h Operation Wind load (survival): - - - • Front thrust • 26.8 kg • Side thrust • 2.2 kg 2.5.2.3.2. 6.5 dBi Panel Electrical Frequency range 902-928 MHz Gain 6.5 dBi (min) VSWR 1.
System Description WipLL Radio Technology - Physical Layer Environmental Test Standard Duration Temperture Notes Low temperature IEC 68-2-1 72 h -55°C - High temperature IEC 68-2-2 72 h +71°C - Temp. cycling IEC 68-2-14 1h -45°C +70°C 3 Cycles Vibration IEC 60721-3-4 30 min/axis - Random 4M3 Shock mechanical IEC 60721-3-4 - - 4M3 Humidity ETSI EN300-2-4 T4.
WipLL Radio Technology - Physical Layer System Description 2.5.2.5. External Antennas For most bands, WipLL products allow connection of a large variety of external antennas. However, WipLL 700 provides a limited variation of external antennas, including, amongst others, the following: 90° panel or omnidirectional (for BSR) 14-element yagi antenna (for SPR) These external antennas can be supplied by Airspan. The external antennas connect to the WipLL devices by an N-type connector. 2.5.2.6.
System Description WipLL Radio Technology - Physical Layer Figure 2-5: Frequency allocation in a four-sector Base Station Radio interference may occur between the BSRs operating in the upper frequency range (i.e., 742 MHz and 744 MHz) and the lower frequency range (i.e., 712 MHz and 714 MHz). To overcome this interference, a 1-meter vertical separation is recommended between the BSRs operating in the upper frequency and the BSRs operating in the lower frequency. 25030311-08 Airspan Networks Inc.
WipLL Radio Technology - Physical Layer System Description 2.5.2.7. Specifications Table 2-4 and Table 2-6 list the external antenna specifications for BSR and SPR devices operating in the 700 MHz band. Table 2-8: BSR 700 MHz external antennas External antenna type 90° panel Omnidirectional Parameter Value Frequency Range (MHz) 698 - 746 Gain (dBi) 14 Beam Width H X V (degrees) 90 x 20 Polarization Vertical VSWR < 1.
System Description WipLL Radio Technology - Physical Layer 2.6. Radio Planning WipLL radio planning can be divided into the following areas: Main technical parameters Coverage analysis Interference analysis: FDD vs. TDD Frequency allocation: Synchronized vs. Unsynchronized operation Capacity considerations Selecting appropriate mode of operation Radio Planning software tool 25030311-08 Airspan Networks Inc.
WipLL Radio Technology - Physical Layer System Description 2.6.1. Main Technical Parameters The main technical parameters required for RF planning for WipLL are summarized in Table 2-10.
System Description WipLL Radio Technology - Physical Layer Parameter Value • ± 4 MHz • 58 dB (60 dB) • ± 5 MHz • 63 dB (64 dB) Receiver Noise Figure 10 dB 2.6.2. System Coverage System coverage includes the following: Line of sight (LOS) Link Budget 2.6.2.1.
WipLL Radio Technology - Physical Layer System Description 2.6.2.2. Link Budget The coverage analysis of WipLL includes the analysis of the power balance between the transmitter and the receiver, threshold considerations, margins, reserves, and certain statistics of the system.
System Description WipLL Radio Technology - Physical Layer 2.6.2.2.1. Propagation loss Propagation is the dispersal of the signal into space as it leaves the antenna. The loss of this propagation depends on the signal path between the transmitter and the receiver. Obstructions in the signal path such as trees and buildings can cause signal degradation. Several models simulate signal attenuation along this path.
WipLL Radio Technology - Physical Layer System Description 2.6.2.2.2. Link Budget Results Based on the previous formulas mentioned in the above sections, the following link budget results can be obtained for 99.9% availability: Modulation Rate (Mbps) Range (in km) 2.4 GHz2 MMDS (2.5 GHz) 3.5 GHz 5.8 GHz 900 MHz 700 MHz 8 FSK 3 or 4 8 8 7 6 8 15 4 FSK 2 11 11 10 8 11 22 2 FSK 1 or 1.
System Description WipLL Radio Technology - Physical Layer 2.6.3.1. FDD vs. TDD Frequency Division Duplex (FDD) interference analysis is relatively simple. The frequency separation between downlink and uplink (50 to 100 MHz) enables Airspan to conduct downlink and uplink interference analysis independently. However, in Time Division Duplex (TDD), since Tx and Rx are not synchronized, cross-link interference, for example, between a transmitting BSR and an adjacent receiving BSR, may result.
WipLL Radio Technology - Physical Layer System Description 2.6.4. Frequency Allocation Frequency allocation includes the following issues: Synchronized vs. Unsynchronized operation Frequency Reuse Frequency Allocation template 2.6.4.1. Synchronized vs. Unsynchronized Operation The frequency allocation scheme in WipLL depends on the mode of operation. Three main options exist: Unsynchronized Frequency Hopping Synchronized Frequency Hopping Fix Sub-Channel Assignment 2.6.4.1.1.
System Description WipLL Radio Technology - Physical Layer Figure 2-7 displays a graph depicting the hit or blocking probability as a function of number of interferers for different table lengths (7, 23, and 79). 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 1 3 5 7 9 N=7 11 13 N = 23 15 17 19 N = 79 Figure 2-7: Hit probability as a function of active interferers Note: The probability of collisions with 20 interferers and 79 sub-channels is only 20%. 2.6.4.1.2.
WipLL Radio Technology - Physical Layer System Description 2.6.4.1.3. Fix Sub-Channel Assignment In some scenarios—mainly licensed bands in which available spectrum is limited— it is possible to create a set of “hopping” tables, each based on a single sub-channel. Using this approach, the hopping nature of the system is actually disabled, so that synchronization is not required.
System Description WipLL Radio Technology - Physical Layer 2.6.5. Capacity Considerations This section provides high-level guidelines for evaluating WipLL capacity. This capacity relates to the number of subscribers supported by a single BSR according to a certain service mix. The methodology presented here provides a simplified approach for evaluating WipLL capacity capabilities.
WipLL Radio Technology - Physical Layer System Description Since voice and data services differ by their packet size and their sensitivity to delay, their protocol efficiency can be substantially different. Therefore, when calculating bandwidth for different applications, the gross bandwidth should be used, which takes into account the protocol efficiency. 2.6.5.2.
System Description WipLL Radio Technology - Physical Layer 2.6.5.4. Calculation Example This example assumes that the required services are based on voice traffic of 100 merlangs per subscriber and a CIR of 256 Kbps. In addition, in this example, a 1% blocking is expected for voice calls, and 1:10 over subscription is expected for data.
WipLL Radio Technology - Physical Layer System Description 2.6.6.1.1. Bit Rate The 1 Msps mode supports three levels of modulation, as presented in Table 2-12. Table 2-12: WipLL bit rate at 1 Msps Modulation Bit/Symbol Bit rate (Mbps) 8-level FSK 3 3 4-level FSK 2 2 2-level FSK 1 1 The 1.33 Msps mode supports two levels of modulation according to Table 2-13. Table 2-13: WipLL bit rate at 1.33 Msps Modulation Bit/Symbol Bit rate (Mbps) 8-level FSK 3 4 2-level FSK 1 1.
System Description WipLL Radio Technology - Physical Layer 2.6.6.2. System Range Considerations System range depends on the maximum output power of the system. Different approaches exist, depending on region and frequency band. 2.6.6.2.1. Unlicensed Bands FCC part 15 (paragraph 247) differentiates between three types of systems: Digital modulated Frequency hopping Hybrid Limitations on Tx (transmit) power and EIRP differ on this basis.
WipLL Radio Technology - Physical Layer System Description The table below lists examples of cable loss per cable for maximum antenna gains, based on the formula above. Note that the EIRP is either equal to or less than 36 dBm. Table 2-15: Example of cable loss per cable for maximum antenna gains Cable type BELDEN 9913 BELDEN 89907 Cable length (ft) Tx power (dBm) Cable loss (dB) 10 18 0.6 30 18.9 100 Max. antenna gain (dBi) Max. EIRP (dBm) 1.5 18.6 18.6 36 36 21.8 4.4 18.
System Description Mode WipLL Radio Technology - Physical Layer Modulation 2 FSK Rate (Mbps) 1.33 Range (Km) 8 Table 2-18: WipLL range at FCC limits for 5.8 GHz Mode 1 Msps 1.33 Msps Modulation Rate (Mbps) Range (Km) 8 FSK 3 2 4 FSK 2 5 2 FSK 1 10 8 FSK 4 1 2 FSK 1.33 8 Note: Link budget is calculated for the uplink assuming free space propagation standard integrated antenna and 10 dB fade margin.
WipLL Radio Technology - Physical Layer System Description 2.6.6.3.1. Intra-system Interference As mentioned previously, 1.33 Msps mode is achieved by using wider channel bandwidth. This results in a higher bit rate at the expense of increasing adjacent channel interference. This difference can become critical mainly for licensed bands in which the available spectrum might be very limited.
System Description WipLL Radio Technology - Physical Layer 2.6.6.3.2. Inter-system Interference The immunity of the WipLL system to external interference is due to its spread spectrum system. Exposure to external interference is highest when operating in the unlicensed band. Both FCC and ETSI set limits on the spreading level that is required by a frequency hopping spread spectrum system.
WipLL Radio Technology - Physical Layer System Description 2.6.6.4. System Capacity The modulation for each link in the WipLL system is adaptively determined according to the signal strength and the BER. When evaluating system capacity, it should be taken into account that the intermediate 4-FSK modulation is not supported when operating at 1.33 Msps. Assume a WipLL deployment where subscribers are located at various distances from the base stations.
System Description WipLL Radio Technology - Physical Layer 2.6.7. Radio Planning Software Tool To design an optimal fixed wireless broadband network, the operator requires an RF design tool that includes features of a geographic information system (GIS) module, a propagation prediction module, and a fixed wireless module.
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