IN THIS ISSUE
September 2005
Vol 5 Issue 3

Feature Article
Predicting the Radio Channel Beyond Second Generation Wireless Systems

Case Corner
Automating Spectrum Management for Rapid Network Design

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by Henry L. Bertoni, ECE Department, Polytechnic University, Brooklyn, NY 11201,
Saúl A. Torrico, Comsearch, 19700 Janelia Farm Boulevard, Ashburn, VA 20147
and George Liang, ECE Department, Utah State University, Logan, UT 84322

Predicting the Radio Channel Beyond
Second Generation Wireless Systems

The design of wireless communication systems beyond second-generation systems requires a detailed understanding of various radio channel parameters, which is usually cast in terms of their statistical distribution. First and second-generation system design required knowledge of the mean received signal and its variability. Third generation and future digital wireless communication systems additionally require knowledge of the delay spread. Operation of wide band code division multiple access (W-CDMA) technology depends on the statistics of multipath components in terms of their number and lifetime for Rake receiver design as shown in Figure 1. Design of smart antennas and other multiple antenna systems, which can improve system capacity or could be used to geo-locate mobiles, make use of the distribution in angle of arrival of the scattered signal.

Figure 1. The number of fingers (a) available at points separated by
2 m along a street, and the CDF (b) of life distance for these fingers.

The foregoing information can be determined from radio surveys, but such surveys are expensive, particularly since they need to be repeated for different antenna heights, and in a number of different building environments. It is advantageous for the system designer to have available a computer-based tool that can be used to predict area coverage, delay spread, angle of arrival, etc. The basis of this tool is a reliable propagation model that accounts for building and terrain data.

Figure 2. Comparison between 908 MHz measurements and prediction
made using the VPL method for the 3D building database of Rosslyn, VA.
Measurements were made using a directive base station antenna
pointing north and located at Tx5 at a height of 42 m.

The ray representation of radio propagation in the UHF band and above provides a physical basis for the multipath description of the received signal used by communications theorists. By tracing the rays and accounting for reflections from buildings and the ground, diffraction at building edges, and non-specular scattering at building surfaces, it is possible to make statistically meaningful predictions of radio channel characteristics. A number of ray tracing codes have been developed for the special conditions of radio propagation in cities, where the building walls are vertical and multiple events (reflections, diffraction or scattering) must be accounted for. Comparison of the predictions generated by one of these codes with measurements show that the small area average power over a region can be computed with mean error of less than 1 dB and standard deviation of about 8 dB, or even less as shown in Figure 2 above. Because the codes give all the physical parameters of the ray paths, they can be used to simulate other properties of interest to system designers, such as the spread in the time delay and angle of arrival of the individual rays as shown in Figure 3 to Figure 5. The statistical distributions of these quantities that are obtained from simulations are found to compare well with those obtained from measurements.

Figure 3. Histograms of building height in three cities.

Ray codes are at the point where inexpensive simulations can be used to test out radio system concepts before more expensive field trials are run. Simulations can help select system parameters, such as the required bandwidth, the number and location of antennas and their directivity, as well as evaluate the effectiveness of signal processing algorithms. Unlike field trials where the entire system is tested with a pass/fail outcome, simulations allow each system feature to be varied in order to see its effect on overall system performance. Another potential application is locating mobiles from signals arriving at a single base station. Presently there are several geo-location techniques used to locate mobiles (i.e. Uplink Time Difference of Arrival (U-TDOA), Cell ID, Assisted-GPS, etc.). As another complementary alternative to improve the accuracy of locating mobiles, we could use an array of antennas and space-time processing to extract the individual ray arrivals, ray codes could trace the rays back to find the common intersection point, which is the mobile location. This application still remains to be evaluated.

Figure 4. Comparison of the cumulative distribution functions of AS
at 900 MHz in the three cities for high base station antennas.

Running time of the ray codes remains a barrier to their use for practical cell system layout, which requires the evaluation of coverage and interference at many locations from several base stations. However, running time limitations may be less severe for the small cells of third and fourth generation networks, and as computers become faster and less expensive. To date, the approaches taken to improve computation time have been to limit the type of rays considered, and to use ideas taken from computer science. The advent of inexpensive multiprocessor systems has also reduced the simulation times through the application of parallel processing techniques.

Figure 5. Comparison of the cumulative distribution functions of AS
at 900 MHz in the three cities for high base station antennas.

In regards to the errors, over distances on the order of 1 km, the errors for ray predictions have standard deviation of 6 - 8 dB, while for shorter distances the error is less. This behavior may be related to the fact that ray paths, like the path of a billiard ball, are chaotic in that the small change in the initial ray direction eventually causes the ray to miss a reflecting wall and subsequently travel along a totally different path (the electromagnetic fields however are not chaotic). It may be that for travel beyond some distance from the base station, the rays become chaotic and give only a statistical measure of the fields. This conjecture remains to be examined.

In conclusion, the design of future wireless communication systems may benefit from a robust computer ray code that could precisely predict the propagation loss between the transmitter and the receiver. The designer could actually understand the spreading of the signal in time and space (angle of arrival) and obtain the number and the life time of the multipath signal. This allows the designer to improve capacity and efficiency of these advanced digital systems. The basis of this robust code is a reliable propagation model that can account for buildings and terrain.

The full article will appear in the IEEE-Antenna Propagation Magazine.

by Brian Eichenser, iQ·link Technical Support Manager

Automating Spectrum Management
for Rapid Network Design

Introduction
If you’ve been in the wireless telecommunications industry for more than 15 years, you might remember drawing a path profile by hand on a topo map. If you’ve been in the industry less than 10 years, you’ll probably chuckle at the notion. Each year, companies are driven by competition to do what they did last year, even faster and more efficiently this year. These are the drivers of many software products in the market today.

The Objective
Precise and efficient spectrum management may well be the most overlooked aspect of wireless network design. Many network designers assume there will always be a frequency they can use. But as a network matures and grows, spectrum can become as scarce as legroom in coach-class. This is where quality software can mean the difference between a timely, reliable network with room to grow or wasted spectrum, time and money.

Frequency Planning
Effective frequency planning methodologies are essential to meet the objective of precise and efficient spectrum management. Comsearch recognized this need in its flagship software product, iQ·link. With one pass through the interference analysis, users can see in one window, a list of every possible channel in the band and an instant answer to the question, "What if I assigned that channel to my link?" By itself, this is already a very powerful, efficient method for assigning frequencies to a link. There’s no need to run several, time-consuming "what-if" scenarios. The software tool summarizes all the "what-if’s", allowing the user to make quick decisions. This has proven to be a very efficient process for some of the world’s largest network operators over the past several years.

Summary section of iQ·link’s Far-Field Interference analysis results window.

Automatic Frequency Planning
In order to keep pace with growing demands, users eventually sought ways to improve upon an already efficient frequency assignment process. We began to ask ourselves, “If a software tool can determine all the what-if scenarios, why can’t it pick the best one? If the software can pick the best one, why can’t it do it for 10, 20 or even hundreds of links at once?” These questions are the basis for Automatic Frequency Planning (AFP).

Automatic Frequency Planning has the potential to significantly improve the efficiency of network rollout and optimization. It allows network designers to consider multiple scenarios, rapidly analyzing the interference impact of an entire design rather than by one link at a time. It can also be very useful for planning upgrades to existing networks to increase capacity or improve efficiencies.

When considering the first phase of this feature, there were two primary issues to solve:

1. When analyzing multiple links at once, how are they assigned a priority?
2. When more than one frequency is available to a link, what is the definition of the "Best" frequency?

The answers to these questions had to satisfy the requirements of multiple operators with varying priorities. Therefore, the user interfaces addressing these issues had to be flexible.

For prioritizing links, an Automatic Frequency Planning tool provides a list of every link that is being analyzed. The user has several options to specify priority:

• Manually, by assigning a number to a link
• In order of Link ID
• In order of Site ID
• According to the Capacity of the link
• According to the modulation of the link
• According to the length of the link

iQ·link’s AFP Prioritization window

Once the list of links is identified and the method of priority is chosen, it’s time to run them through a detailed interference analysis. At this point, it’s necessary to define the user’s idea of the “Best Frequency”. For some, it might be the frequency with the least total interfering level. For others, it’s the frequency that can be reused the most, pushing the interference objective to its limits. And still others, it might be one of three, off-the-shelf radios that are pre-tuned to a specific frequency. AFP provides the user with the options to accommodate these varying requirements.

Following the analysis, AFP provides a report of the links that had frequencies assigned and those that could not meet the objectives. Before making any permanent changes to the network design, the user can decide what to accept and what needs further investigation.

iQ·link’s AFP Report Summary Window

Any change accepted by the user becomes part of the master database and will be considered as part of any future analysis.

Conclusions
The industry is determined to bring new wireless services to the market in a rapid fashion and demands tools that deliver. There is no shortage of ideas for improving AFP, which is now in its 2nd revision with iQ·link version 8.3 delivered this summer. With this revision, we incorporated a new, sophisticated algorithm for automatically resolving High / Low frequency plan conflicts on all of the links prior to analysis. This is one more time-consuming step the network designer doesn’t need to worry about. For future releases, there are many improvements being considered, including additional priority options, the ability to recommend antenna upgrades to resolve interference, automatically choosing an appropriate frequency band, sizing antennas, setting transmit power to meet availability objectives, etc. All of these improvements have one goal in mind – timely deployment without sacrificing spectrum efficiency.

This type of interference mitigation software is also finding its way off the desktop and into the field. In the not so distant future, software-defined radios, with built-in Automatic Frequency Planning, will play a large role in facilitating rapid rollout of new technologies, while continuing to make the best use of the available spectrum.

MICROWAVE

Canada and U.S. to Facilitate Deployment of Border Public Safety Services in the 764-776 and 794-806 MHz Bands - DOC-259427A1.pdf

FCC Delays Effective Date for Rules Concerning Unsolicited  Fax Advertisements - New Implementation Date is January 9, 2006.  (Dkt No 02-278, FCC No. 05-132) DOC-259689A1.pdf   FCC-05-132A1.pdf

Licensing Procedures Announced to Facilitate the Transition of BAS, CARS, and LTTS Licenses to the 2025-2110 MHz Band -  (DA No.  05-2223) DA-05-2223A1.pdf

Universal Licensing System Changed to Implement the Immediate Approval Procedures for Wireless License Assignments and Transfers - (DA No.  05-2226)   DA-05-2226A1.pdf

FCC Adopts Policy Statement - New Principles to Preserve and Promote the Open and Interconnected Nature of Public Internet.  DOC-260435A1.pdf 
DOC-260435A2.pdf

FCC Requires Certain Broadband and VOIP Providers to Accommodate Wiretaps - DOC-260434A1.pdf  DOC-260434A2.pdf  DOC-260434A3.pdf

Biennial Regulatory Review - Amendment of Parts 1, 22, 24, 27, and 90 to Streamline and Harmonize Various Rules Affecting Wireless Radio Services - (Dkt No.  03-264, FCC No. 05-144) FCC-05-144A1.pdf  FCC-05-144A2.pdf

Service Rules For Advanced Wireless Services in the 1.7 and 2.1 GHz Bands - The FCC moved to make spectrum available for an array of innovative wireless services and technologies, including voice, data, video, and other wireless broadband services offered over Third Generation ("3G") mobile networks. (Dkt No.  02-353, FCC No. 05-149) FCC-05-149A1.pdf FCC-05-149A2.pdf  FCC-05-149A3.pdf  FCC-05-149A4.pdf  DOC-260432A1.pdf  DOC-260432A2.pdf  DOC-260432A3.pdf

FCC Releases "Trends In The International Telecommunications Industry" Report -  DOC-261024A1.pdf  DOC-261024A2.pdf

SATELLITE

International Bureau Extends Comment Period in Satellite Space and Earth Station Licensing Reform Proceeding (IB Docket No. 00-248) for Interested Parties Impacted by Hurricane Katrina

On March 10, 2005, the Commission adopted a Third Notice of Proposed Rulemaking in its ongoing efforts to modernize and reform space station and earth station licensing. Specifically, the Commission sought comment on proposed revisions to Part 25 of the Commission’s rules that should give earth station operators in the fixed-satellite service more flexibility in implementing state-of-the-art earth stations in the Fixed Satellite Service (FSS) in the conventional C-band and Ku-band.

Currently, comments in this proceeding are due on September 6, 2005, and reply comments are due October 6, 2005. As a result of the devastation caused by Hurricane Katrina in certain areas within the states of Louisiana, Mississippi, and Alabama, the International Bureau is extending the comment date for interested parties and/or their counsel located in the affected areas from September 6, 2005 to September 28, 2005. Replies responsive to issues raised in late-filed comments may be filed on October 14, 2005.

Intelsat Set To Become Largest Satellite Operator With Acquisition Of Panamsat

Intelsat Ltd. has agreed to acquire Panamsat for $3.2 billion to create the world's largest Fixed Satellite Services company. The combined company, which will retain the name Intelsat, will operate a fleet of 53 satellites and generate more than $1.9 billion in annual revenue. Under the agreement, announced Aug. 29, shareholders of Panamsat Holding Corp. will receive $25 per share, nearly 40 percent above the company's March initial public offering price. Intelsat also will assume $3.2 billion in debt held by Panamsat and its subsidiaries. Intelsat's deal with Panamsat trumps a reported combination with New Skies Satellites. The deal is expected to close by August 2006, dependent on U.S. government approval.

Chief of Satellite Division, FCC’s International Bureau Retires

Goldberg, Godles, Wiener & Wright announced that Thomas Tycz would become the firm's senior policy advisor, effective Sept. 19.

Tycz recently retired from the U.S. Federal Communications Commission (FCC) from his position as chief of the satellite division in the FCC's International Bureau. He spent more than 30 years at the FCC in various executive positions.

Satellite Operators Contribute to Katrina Disaster Relief

Numerous Satellite Operators have joined forces and have been involved in the relief effort following the aftermath of hurricane Katrina. They have been able to provide rapid data management collection capabilities and mobile satellite communications to elements of the 2nd U.S. Marine Expeditionary Force and the Federal Emergency Management Agency (FEMA), which currently are assisting victims of Hurricane Katrina. Globalstar announced Sept. 6 it has deployed more than 10,000 handheld satellite phones to customers in the Gulf region, primarily to government agencies and relief workers, within the first week following the Aug. 29 landfall of Hurricane Katrina. Globalstar said it increased the capacity of its satellite network to ensure continued communications service to the region.

Federal Geographic Data Committee Issues Guidelines On Offering Satellite Imagery

The Federal Geographic Data Committee of the U.S. Geological Survey (USGS) published guidelines intended to set standard procedures for governing the dissemination of geospatial imagery.

The guidelines "are directed at organizations that originate geospatial data and are interested in disseminating data publicly but are concerned that such actions may pose a risk to security." Services such as Google Earth, which offers free satellite imagery, among other things, via the Web, would fall under these guidelines.

According to the committee document, "dissemination is essential to the mission of many organizations and the majority of these data are appropriate for public release. However a small portion of these data could pose risks to security and may therefore require safeguarding."

A copy of the guidelines can be found on the committee's Web site at http://www.fgdc.gov/fgdc/homeland/access_guidelines.pdf

Comsearch Supports Microwave Licensees Impacted by Hurricane Katrina
Restoring microwave communications in the gulf region has become a mission for U.S. Wireless Operators. Since the storm, Comsearch has been providing around the clock support and expedited services to help facilitate re-building the wireless infrastructure in the hurricane ravaged areas of the country. Carriers have also turned to Comsearch’s comprehensive databases to recreate system data lost during the hurricane.

"We understand the importance of this massive recovery effort," said Chris Hardy, Vice President and General Manager for Comsearch. "The severity of Hurricane Katrina lead to significant disruption of wireless services and Comsearch will continue to do its part to help wireless operators quickly restore services to the devastated gulf region."

For more information on Comsearch’s microwave services, please contact us at customersupport@comsearch.com.

Comsearch Releases iQ·link® Version 8.3.07
Following the release of iQ·link Version 8.3 in May of this year, Comsearch has released a patch, offering several customer-requested enhancements. Included in this release are improvements in the handling of co-channel / cross-pol links, the ability to specify coordinates at the antenna level, an improved High/Low conflict check based on a user-defined radius, and the ability to hide obsolete equipment as well as other minor improvements to the User Interface.

The Comsearch iQ·link® User Conference is Scheduled for December 1 – 2
Comsearch, together with Eplus, is hosting its 6th annual user conference in Düsseldorf, Germany. The iQ·link User Conference provides iQ.link customers a forum to discuss common interests related to microwave planning and regulatory issues, with an opportunity to see the latest iQ·link features and to provide input on future releases. For more information, email Brian Eichenser at Brian.Eichenser@comsearch.com.

Comsearch to Exhibit at the Society of Broadcast Engineers 2nd Annual Broadcast Engineering Expo & SBE National Meeting in Grapevine, Texas, October 19-20
Please visit us at booth #4 to learn more about our spectrum management services including frequency coordination and protection services for broadcasters, broadcast and microwave license management services, field services and our BAS 2 GHz transitioning services.

For more information on the SBE 2005 Annual Expo, visit www.sbe.org and click on Conferences & Conventions in the left menu.

Comsearch Article on 71-95 GHz Registration Gets Published in Mission Critical Communications, September 2005 Issue
"71-95 GHz Registration – Light Licensing with Interference Protection", written by Laura Fontaine, Director, Spectrum Management Services for Comsearch, addresses the FCC allocation and availability of high-quality multi-gigabit point-to-point spectrum for new and emerging broadband applications and the industry-managed device-registration process which streamlines licensing procedures and protects against interference.

Comsearch Selected, for the 8th Year in a Row, to Serve as the Official Frequency Coordinator for CTIA Wireless I.T. and Entertainment 2005 in San Francisco, CA, September 27-29, 2005
Comsearch has developed a spectrum management process that efficiently addresses the interference and coordination issues for temporary wireless demonstrations. Using our frequency analysis software, iQ·clear®, and engineering expertise, Comsearch is able to coordinate with PCS licensees in the area, analyze potential interference and coordinate frequencies with microwave incumbents, coordinate frequencies between exhibitors and monitor for on-site interference. Click here for more information on Comsearch’s Frequency Coordination for Trade Shows.

Comsearch Offers Protection Services to 6.1 GHz Terrestrial Microwave Facilities Operating Near the Coast, a Waterway, or Harbor!
The FCC’s January 31, 2005 ruling granting primary status to shipboard earth stations allows them to transmit on frequencies that are co-channel with microwave receivers near the waterways, thus increasing the potential for RF interference.

Comsearch’s 6.1 GHz Terrestrial Microwave Protection Services help ensure that your systems are free of interference and any potential problems with other systems are identified during the coordination process.

To find out more about Comsearch’s Coordination and Frequency Protection Services or about the FCCs ESV rulemaking contact Denise Finney at customersupport@comsearch.com or at 800-318-1234.

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