Written by Brian Jones of EDX Wireless, Inc.

Introduction

EDX has been a leader in land-mobile radio and DMR planning since it was founded in 1985. The core SignalPro software includes a collection of studies meant to address the special challenges involved in planning simulcast networks, as well as heterogeneous networks that include both simulcast and multicast regions. These studies can be found both in the basic study group and also in the study group called TSB-88.

The U.S. Telecommunications Industry Association (TIA) publishes and updates a large and complex document called the Telecommunications Systems Bulletin-88, known as TSB-88, which gives a variety of recommendations for mobile radio planning. This document provides information and advice to manufacturers and users of primarily Land Mobile and Public Safety radio systems. It provides guidance on performance criteria for different types of radio technologies and methods for measuring and predicting system performance. Section 5 of the TSB-88.1 document provides several suggested methods for predicting system performance and reliability over a defined area. The document provides various options for performing an analysis and it is up to each person to decide how to proceed. Further, new methods and recommendations are periodically added in updated versions of the document.  

EDX has continually maintained and added to its complement of studies over the years. The EDX TSB-88 studies section is based on EDX’s interpretation and implementation of the TSB-88 recommendations and on what the majority of our U.S. land mobile radio customers have requested over the decades that we’ve offered these features. 

In 2009 EDX released version 1 of its TSB-88 Monte Carlo studies, designed to take fading and simulcast delay-spread into account within the same analysis. These studies were designed in collaboration with the TSB-88 committee and in accordance with the recommendations given in TSB-88.1-C; Appendix E, which has also gone through multiple revisions since its original release. 

 The summer 2025 release of SignalPro further includes three new updated (Version 2) TSB-88 Monte Carlo studies. With all these study options available, knowing which studies to choose and how to set them up can be confusing. This document looks at the various simulcast-related studies, clarifies the differences between them, and suggests some best practices for simulcast planning within EDX SignalPro.

Why simulcast networks require specialized studies

Land-mobile communications often use simulcast networks in areas where terrain shadowing makes it difficult to reliably cover the entire area with just one site. A simulcast network has multiple base stations, often including tall macro sites and low power repeaters to fill in difficult spots, with all base stations transmitting the same signal on the same frequency. This effectively creates one large “cell” or simulcast group operating on a single radio frequency. As a mobile unit moves through the area and experiences signal fading from one base station, the signal from other base stations effectively reinforce the desired signal to provide seamless reliable coverage. 

For these co-channel signals from various base stations to reinforce each other at the mobile receiver they must be reasonably aligned in the time domain. The mobile receiver locks onto the timing of the strongest incoming signal at its location and other incoming signals arrive with some difference in transit time from the strongest. If this difference in arrival time is too great, then the delayed signal no longer reinforces coverage, but becomes a source of interference by distorting the desired signal. If the various incoming signals at a receiver have a large difference in arrival time but similar power levels, then it can cause time-delay interference (TDI), negatively impacting intelligibility. 

This feature of simulcast networks means that they require special planning techniques to ensure reliable coverage. In general, the goal is to ensure reliable coverage even with substantial signal fading but also ensure that the delay-spread, or difference in arrival time between the strongest and other incoming simulcast signals, remains below the maximum allowable value to prevent time-delay interference.

Definition of terms

The Challenge:
Modeling the Relationship Between Coverage Fading and TDI

In earlier revisions of both the TIA TSB-88 and EDX SignalPro, the recommended planning practices for simulcast networks treated coverage fading and delay-spread as two different issues, using separate studies to account for them. Coverage studies were typically run using a very conservative propagation model that assumed some excess pathloss margin to represent a faded or worst-case received signal power at the remote site. Then, running delay-spread studies showed the delay-spread values for all those areas where the receiver had more than one signal within the capture ratio. If a given location showed too high a delay-spread value, then that location would be considered unreliable due to the high potential for TDI at that location. The limitation of this method, though, is that incoming signal levels in the real world constantly change due to Rayleigh fading and the slow fading caused by the mobile’s moving through the environment. By using a conservative propagation model to establish coverage and then treating time-delay separately, it’s possible to overlook areas of marginal reliability where TDI only occurs under certain signal fading conditions. 

EDX developed the TSB-88 area studies and added them to SignalPro in collaboration with the TIA TSB-88 committee as a more sophisticated method of evaluating the potential for TDI under dynamic signal fading conditions. EDX developed version 1 of our TSB-88 studies in coordination with committee members. The TSB-88 document itself was later revised to include recommendations for a similar Monte Carlo approach. 

The TSB-88 Monte Carlo studies in EDX SignalPro offer a few ways of looking at the potential for TDI and finding the overall predicted reliability of downlink reception in a simulcast network. These studies run a Monte Carlo simulation where the signal levels from all relevant base stations are allowed to fade up and down over a given number of trials. In each trial the time-delay values and relative power levels are evaluated to determine whether the receiver would perform adequately and the percentage overall reliability or a related metric are produced as an area study layer. 

Note: There is also a full selection of uplink studies for land-mobile systems with different voting and diversity schemes. This document covers only the downlink studies related to simulcast. For a full description and best-practices regarding uplink studies, be sure to visit the EDX knowledge base or Reference Manual Appendices.

Describing sector and mobile properties

Take care to provide correct link budget and antenna details for all sectors (base stations) and also for the mobile/remote used for the studies. Each sector has a value for the simulcast delay offset, which delays the effective launch time of the signal from that sector. The default value is zero; only increase it if you want to delay that sector’s launch time to better align with other sectors. 

Open

Transmitter/Sector properties Fields – Link Budget, Antenna Details

Configure the mobile/remote unit(s) used in the study with the correct antenna gain, height, etc. (Pay careful attention to the Receiver simulcast capture ratio range.) Delayed signals within the capture ratio range potentially can cause TDI, so it’s important to establish the correct value based on the equipment, modulation, and DAQ requirement.

Open

Receiver Configuration Fields

It’s also possible to define the performance of the receiver under different signal-to-noise and delay conditions. The Monte Carlo analysis can be run using a simple static requirement for CPC and delay-spread or it can be run using a simulcast curve file. This file gives a table of delay-spread values and the CPC ratio needed to achieve the desired performance. 

Open

Data Editor Dialog

To create this file, go to Utilities > Create/Edit Simulcast Curve File.
Note: The Hess Simulcast Monte Carlo Reliability study requires this file. Other simulcast studies use a single CPC and delay-spread criteria.

Propagation model considerations; average vs faded coverage predictions

SignalPro includes a number of propagation models appropriate for any land-mobile frequency band. For land-mobile planning, users typically choose a path-based deterministic model such as Anderson2D, Longley-Rice, or Free Space + RMD. For all models, one important consideration is whether the model should be set up to target the average signal level or a faded signal level.

Previous versions of the TSB-88 document recommended including additional pathloss margins as part of the propagation model to account for both fast fading and seasonal fading. This was usually done using the % of Location and % of Time fields, which add more pathloss to the model to account for fading. This produces a smaller coverage footprint around the site to represent the signal level in a faded or worst-case condition. Since the average real-world signal level at any location should always be higher than the prediction, this method is not ideal for evaluating the potential for interference. 

The TSB-88 Monte Carlo analyses designs take fading into account within the study itself, so typically the propagation model setup should target the average signal level that would be measured in the field, rather than a faded signal level. This means that, when running the Monte Carlo analysis,  the % of Location and % of Time fields should be set to 50, meaning no additional pathloss. 

A typical propagation model configuration for VHF or UHF simulcast coverage would be the Anderson2D model with the add clutter loss option turned on and the % of Time and Location fields set to 50%,  similar to the following:

Open

Propagation Models Dialog

Any clutter database should include a clutter attenuation file, which gives default clutter loss values for each clutter type and frequency band. EDX-provided attenuation files base these values on TSB-88 recommendations for general clutter losses. Any given project area may need to have those clutter loss values adjusted to get the most accurate prediction possible. Do this using field measurement (drive test) data and the ‘Test Against Measurements’ function. Model tuning-and-validation is an important step to ensure an accurate prediction. While the default values may be acceptable in many regions (especially within the United States, where the recommendations were developed), it’s important to consider the project area carefully and decide whether clutter in the project area necessitates drive testing and model tuning. For additional information on model tuning and validation, see the EDX Knowledge Base.

TSB-88 Monte Carlo Study Set-up

After setting up equipment parameters and the propagation model, add area studies to the project and run them. If using any of the area studies in the TSB-88 study group, it’s important to set up the performance criteria and Monte Carlo settings in the Studies > TSB-88 Studies Setup, similar to the following:

Open

TSB-88 System Study Setup Dialog

Simulcast Study types

The following section provides a brief description of each of the simulcast-related downlink area studies in SignalPro. A more complete explanation of the propagation model methods and area study method can be found in the Reference Manual Appendices. This list is meant as a quick reference to clarify some of the differences between them.

Which Monte Carlo Studies Apply?

Choosing and interpreting studies are always engineering decisions requiring a complete understanding of the network’s real-world requirements and the study types available. EDX updated the analysis, but left the previous versions of the TSB-88 Monte Carlo studies intact so that users can continue with the original method for established projects or reproduce previous results. EDX Engineering believes improved Monte Carlo analysis provides more realistic and accurate simulcast performance in most situations when using proper inputs. 

If populating the Simulcast Curve File with signal vs. delay values then the most complete reliability prediction is the ‘Hess Simulcast Monte Carlo Reliability (updated).’ If using only a single requirement for CPC and delay spread then EDX recommends the ‘Aggregate Simulcast Monte Carlo Reliability (updated).' 

To produce a layer showing the generalized delay spread in microsends for each location, EDX recommends the ‘Simulcast Delay Spread (Hess),’ particularly in environments that may exhibit high multipath, such as urban canyons or rugged terrain. 

Including interference from outside sources (neighboring networks)

Exclusive to the updated (Version 2) Bounded Area Coverage and Aggregate Reliability studies, correct configurations consider not only simulcast time-delay interference from transmitters in the same simulcast group, but also interference from other non-coordinated sources in a second group. For example, if two adjacent network operators use the same frequency, then in-network sites may generate TDI but nearby out-of-network sites /cause traditional cochannel interference (regardless of timing considerations). To represent this in a SignalPro project, put all the coordinated simulcast sectors into one Tx Group set as the Primary Tx group in the study details. Then put sectors from the uncoordinated interfering network into another Tx group set as the secondary Tx group in the study details. The reliability percentage calculated by the study takes interference from the second group into account when calculating the CPC. This is an important feature for modelling the potential for inter-network interference and how it might degrade an otherwise reliable simulcast system.

Document # 08-SP13.0.26-0R0

© 2025, EDX Wireless, Inc. All Rights Reserved.