Chapter 2 Background
Chapter 2 presents the necessary background and research on which the SSTDSP sounder was developed and is divided into two major sections: Propagation at LMDS and Channel Sounding.
Propagation at LMDS
The following section presents the fundamental theory behind propagation of wireless signals in the LMDS band.
What is LMDS?
To better understand the need for the SSTDSP sounder system, further explanation of LMDS is necessary. The acronym LMDS stands for “Local Multipoint Distribution Service” and was created by the Federal Communications Commission (FCC) to describe a two-way digital wireless communications medium that can carry voice, data, and video simultaneously . The primary Block A LMDS spectrum license obtained by Virginia Tech ranges from 27.5 GHz to 28.35 GHz, a total of 850 MHz of continuous spectrum. The primary LMDS Block B license defined by the FCCC extends from 31.075 to 31.225 GHz, a total of 150 MHz of continuous spectrum. LMDS is considered a millimeter frequency, given its approximately 11mm wavelength. When properly deployed, LMDS networks may utilize this large block of spectrum for high-speed communications and data transfer up to several Gbit/sec. Equipment manufactors are currently claiming that they have product offerings that can provide 622 Mbps. In comparison, upcoming 3G mobile wireless systems may permit transfer speeds of several Mb/sec. This allows LMDS fixed wireless point to point and point to multi-point links to be used as effective “wireless fiber” backbones reaching geographic areas that are uneconomical to reach with landline connections such as fiber optics and cable.The network topology of an LMDS system is similar to that of mobile cellular radio networks, however the size of the cells are much smaller, often four to five kilometers. The size of these cells is a function of the range of the LMD equipment, which is heavily influenced by the high propagation path loss and large noise power inherent to millimeter systems such as LMDS. The higher frequencies present in LMDS systems
increase the propagation path loss and receiver noise figure; however, the true limitation of broadband wireless systems that utilize LMDS is the large system bandwidth. In the link budgets developed and calculated in this thesis, the large system bandwidth increased the kTB noise power. This phenomenon is further explained in the following sections.Geographic regions are divided into cells, each with a centrally located hub and multiple receivers or transceivers used by subscribers. Point to point links can be used to link hub to hub using highly directional antennas, while point to multipoint links are used to link hubs with sectored antennas to the local subscribers with highly directional antennas.
This user/hub topology can be considered a “star architecture,” where one main node serves as the gateway to the outside world. LMDS systems could also be configured in a”mesh architecture,” where each node can talk directly to each other without going through a hub. This is more complicated to implement requiring network coordination and innovation multiple access and routing schemes.
1.1 CONTENT AND ORGANIZATION OF THESIS
1.4 PROBLEM DEFINITION
2.1 PROPAGATION AT LMDS
2.1.1 What is LMDS?
2.1.2 What is Unique about LMDS?
2.1.3 Wireless Propagation At LMDS Frequencies
2.1.4 Free Space Path Loss for LMDS
2.1.5 Link Budget for LMDS
2.1.6 Refraction, Reflection, Scattering, and Diffraction
2.1.7 Fresnel Zone Clearance
2.1.8 Is There a Bounce at LMDS?
2.2 CHANNEL SOUNDING.
2.2.1 Channel Modeling at LMDS
2.2.2 Channel Metrics for LMDS
2.2.3 Channel Sounding History and Methods
3 DESIGN AND IMPLEMENTATION
3.1 SYSTEM REQUIREMENTS
3.1.1 Review of system parameters
3.1.2 Tradeoff analysis
3.1.3 Channel Metric calculation considerations
3.2 POWER CONSIDERATIONS
3.2.1 Peak and Average Power of a Short Pulse
3.2.2 Peak to average power ratio
3.2.3 Link Budget
3.3 SYSTEM OVERVIEW
3.3.1 List of SSTDSP sounder modules and system block diagram
3.3.2 List of SSTDSP sounder algorithms and scripts
3.3.3 Functional description of SSTDSP sounder hardware
3.4 MODULE DETAILS
3.4.1 TX Host Control Module
3.4.2 TX and RX Frequency and Location Modules
3.4.3 TX Pulsar Module
3.4.4 TX LMDS Radio Module
3.4.5 RX LMDS Radio Module
3.4.6 RX IF Sampler Module
3.4.7 RX DSP Module
3.4.8 RX Host Module
3.4.9 TX and RX Power Module
3.5 ALGORITHM DETAILS
3.6 SCRIPT DETAILS
4 CHANNEL MEASUREMENT AND RESULTS
4.1 REVIEW OF SSTDSP SOUNDER MEASUREMENTS
4.2 CALIBRATION AND VERIFICATION PROCESS
4.3 TEST PROCEDURE FOR TAKING SSTDSP SOUNDER MEASUREMENTS
4.4 PRESENTATION AND ANALYSIS OF MEASUREMENT DATA
4.5 WORK IN PROGRESS
4.5.1 Completion of RX IF Sampler and LMDS channel measurement
4.5.2 SSTDSP sounder measurement campaign
4.5.3 Future SSTDSP sounder upgrades and improvements
5 CONCLUSION AND FUTURE IMPLICATIONS
A MODULE INTERFACES, OPERATION, AND KEY PARAMETERS
A.1 TX HOST CONTROL MODULE
A.2 TX AND RX FREQUENCY AND LOCATION MODULES
A.3 TX PULSAR MODULE
A.4 TX LMDS RADIO MODULE
A.5 RX LMDS RADIO MODULE
A.6 RX IF SAMPLER MODULE
A.7 RX DSP MODULE
A.8 RX HOST MODULE
A.9 TX AND RX POWER MODULE
B ALGORITHM LANGUAGE AND PROCESSING FLOW DETAILS
C MODULE PHOTOS AND ALGORITHM SOURCE CODE
D DETAILS OF TEST PROCEDURE FOR TAKING SSTDSP SOUNDER MEASUREMENTS