https://urgentcomm.com/wp-content/themes/ucm_child/assets/images/logo/footer-new-logo.png
  • Home
  • News
  • Multimedia
    • Back
    • Multimedia
    • Video
    • Podcasts
    • Galleries
    • IWCE’s Video Showcase
    • IWCE 2022 Winter Showcase
    • IWCE 2023 Pre-event Guide
  • Commentary
    • Back
    • Commentary
    • Urgent Matters
    • View From The Top
    • All Things IWCE
    • Legal Matters
  • Resources
    • Back
    • Resources
    • Webinars
    • White Papers
    • Reprints & Reuse
  • IWCE
    • Back
    • IWCE
    • Conference
    • Special Events
    • Exhibitor Listings
    • Premier Partners
    • Floor Plan
    • Exhibiting Information
    • Register for IWCE
  • About Us
    • Back
    • About Us
    • Contact Us
    • Advertise
    • Terms of Service
    • Privacy Statement
    • Cookie Policy
  • Related Sites
    • Back
    • American City & County
    • IWCE
    • Light Reading
    • IOT World Today
    • Mission Critical Technologies
    • TU-Auto
  • In the field
    • Back
    • In the field
    • Broadband Push-to-X
    • Internet of Things
    • Project 25
    • Public-Safety Broadband/FirstNet
    • Virtual/Augmented Reality
    • Land Mobile Radio
    • Long Term Evolution (LTE)
    • Applications
    • Drones/Robots
    • IoT/Smart X
    • Software
    • Subscriber Devices
    • Video
  • Call Center/Command
    • Back
    • Call Center/Command
    • Artificial Intelligence
    • NG911
    • Alerting Systems
    • Analytics
    • Dispatch/Call-taking
    • Incident Command/Situational Awareness
    • Tracking, Monitoring & Control
  • Network Tech
    • Back
    • Network Tech
    • Interoperability
    • LMR 100
    • LMR 200
    • Backhaul
    • Deployables
    • Power
    • Tower & Site
    • Wireless Networks
    • Coverage/Interference
    • Security
    • System Design
    • System Installation
    • System Operation
    • Test & Measurement
  • Operations
    • Back
    • Operations
    • Critical Infrastructure
    • Enterprise
    • Federal Government/Military
    • Public Safety
    • State & Local Government
    • Training
  • Regulations
    • Back
    • Regulations
    • Narrowbanding
    • T-Band
    • Rebanding
    • TV White Spaces
    • None
    • Funding
    • Policy
    • Regional Coordination
    • Standards
  • Organizations
    • Back
    • Organizations
    • AASHTO
    • APCO
    • DHS
    • DMR Association
    • ETA
    • EWA
    • FCC
    • IWCE
    • NASEMSO
    • NATE
    • NXDN Forum
    • NENA
    • NIST/PSCR
    • NPSTC
    • NTIA/FirstNet
    • P25 TIG
    • TETRA + CCA
    • UTC
Urgent Communications
  • NEWSLETTER
  • Home
  • News
  • Multimedia
    • Back
    • Video
    • Podcasts
    • Omdia Crit Comms Circle Podcast
    • Galleries
    • IWCE’s Video Showcase
    • IWCE 2023 Pre-event Guide
    • IWCE 2022 Winter Showcase
  • Commentary
    • Back
    • All Things IWCE
    • Urgent Matters
    • View From The Top
    • Legal Matters
  • Resources
    • Back
    • Webinars
    • White Papers
    • Reprints & Reuse
    • UC eZines
    • Sponsored content
  • IWCE
    • Back
    • Conference
    • Why Attend
    • Exhibitor Listing
    • Floor Plan
    • Exhibiting Information
    • Join the Event Mailing List
  • About Us
    • Back
    • About Us
    • Contact Us
    • Advertise
    • Cookie Policy
    • Terms of Service
    • Privacy Statement
  • Related Sites
    • Back
    • American City & County
    • IWCE
    • Light Reading
    • IOT World Today
    • TU-Auto
  • newsletter
  • In the field
    • Back
    • Internet of Things
    • Broadband Push-to-X
    • Project 25
    • Public-Safety Broadband/FirstNet
    • Virtual/Augmented Reality
    • Land Mobile Radio
    • Long Term Evolution (LTE)
    • Applications
    • Drones/Robots
    • IoT/Smart X
    • Software
    • Subscriber Devices
    • Video
  • Call Center/Command
    • Back
    • Artificial Intelligence
    • NG911
    • Alerting Systems
    • Analytics
    • Dispatch/Call-taking
    • Incident Command/Situational Awareness
    • Tracking, Monitoring & Control
  • Network Tech
    • Back
    • Cybersecurity
    • Interoperability
    • LMR 100
    • LMR 200
    • Backhaul
    • Deployables
    • Power
    • Tower & Site
    • Wireless Networks
    • Coverage/Interference
    • Security
    • System Design
    • System Installation
    • System Operation
    • Test & Measurement
  • Operations
    • Back
    • Critical Infrastructure
    • Enterprise
    • Federal Government/Military
    • Public Safety
    • State & Local Government
    • Training
  • Regulations
    • Back
    • Narrowbanding
    • T-Band
    • Rebanding
    • TV White Spaces
    • None
    • Funding
    • Policy
    • Regional Coordination
    • Standards
  • Organizations
    • Back
    • AASHTO
    • APCO
    • DHS
    • DMR Association
    • ETA
    • EWA
    • FCC
    • IWCE
    • NASEMSO
    • NATE
    • NXDN Forum
    • NENA
    • NIST/PSCR
    • NPSTC
    • NTIA/FirstNet
    • P25 TIG
    • TETRA + CCA
    • UTC
acc.com

Wireless Networks


Not your father’s radio network

Not your father’s radio network

Managing broadband capacity in a packet-based world requires a new mindset
  • Written by Urgent Communications Administrator
  • 1st January 2008

Modern land mobile radio systems are packet-switched networks that contrast sharply with legacy systems using circuit-switched connections. The circuit switch operates like the original telephone network, where each call requires a physical connection between two end users that is maintained until the call is complete. The circuit switch manages some number of narrowband channels, and each channel is dedicated to a single conversation for the duration of the call. A trunked radio network is an example of a circuit-switched network.

In contrast, the packet switch manages a single broadband channel by time-sharing the channel on a packet-by-packet basis. Access is controlled using a multiple access method such as carrier sense multiple access with collision avoidance (CSMA/CA). Computer professionals often call the broadband channel the medium, and methods for controlling the medium fall into a class of protocols called medium access control (MAC).

In packet networks, a single message or conversation is divided into many packets that typically are interleaved in time with packets from other users. Packets from the same conversation can arrive at different times and even out of order. The uncertain delivery time makes packet-switched networks less suitable for voice traffic, but special protocols used by voice-over-IP (VoIP) systems prioritize voice packets so they are assembled more quickly and cause no noticeable delays to the user. IEEE 802.11 (Wi-Fi) networks are packet-switched networks.

Circuit switching is inefficient for bursty traffic, but push-to-talk voice calls — and all data calls — are inherently bursty. Furthermore, practically all computer networks are packet-switched. Eventually, the convergence of computer and radio technology will draw all radio traffic into packet-switched networks. This article examines the protocols used on packet-switched radio networks and the methods for managing bandwidth on these networks.

The OSI model

Most computer networks follow the reference model for open systems interconnection (OSI) as published by the International Standards Organization (ISO). The OSI model has seven layers that communicate between end systems. The user generates a message at the top layer called the application layer (layer 7), and the message moves down the protocol stack to the physical layer (layer 1), where the message is physically transmitted over the communications medium (cable or radio). At the distant end, the message moves up the stack until it reaches the corresponding application layer.

Intermediate nodes in an OSI network require only the bottom layer functions of the OSI model. For example, if our network is a packet radio system, the network node or base station needs to implement only the physical, data link and network layers. Such a configuration is shown in Figure 1. Note that we are using the normal convention of arrows between equivalent layers. These arrows indicate a virtual connection except at the physical layer, where there is an actual connection. Messages must travel down the stack and across the channel at the physical layer.

Computer networks almost universally operate under a somewhat different model called the TCP/IP model. Unlike the OSI model, the TCP/IP model is not an international standard, and its definitions are somewhat different. The TCP/IP model has five layers, with the first four layers identical to the OSI model. The fifth layer, called application, combines the session, presentation and application layers of the OSI model.

When computer professionals speak of bandwidth management, they mean management of a medium characterized by some gross bit rate, whether it originates from a radio network or a landline network. When radio professionals speak of bandwidth management, they usually mean spectrum management, which is the efficient use of allocated radio spectrum shared by multiple users.

Bandwidth management (computers)

Information technology (IT) professionals are familiar with the many tools and techniques for managing network bandwidth. However, a good reference resource for obtaining more details on bandwidth management in computer networks is How to Accelerate Your Internet, edited by Rob Flickenger, which is available for free from http://bwmo.net.

Spectrum management (radios)

The goal of spectrum management is to maximize users per MHz per square kilometer while maintaining some minimum service threshold. The service threshold may have multiple parts that apply simultaneously, such as minimum signal strength, maximum probability of call blocking, minimum subjective voice quality (e.g., DAQ = 3.4) and minimum throughput.

To illustrate good spectrum management in a packet radio network, let’s use 802.11b as an example. Assume that the service area cannot be covered by a single access point (AP) because one AP cannot provide adequate radio coverage or support the expected number of simultaneous users. Given these assumptions, we face two constraints:

  • Spatially adjacent co-channel APs will create dead zones between cells where service will be unsatisfactory unless the network is lightly loaded.
  • Only three non-overlapping 802.11 channels exist in the 2.4 GHz band: Channel 1 at 2412 MHz, Channel 6 at 2437 MHz and Channel 11 at 2462 MHz.

One way to address these constraints is to borrow a concept from cellular phone networks and use an N=3 frequency reuse pattern, which is illustrated in Figure 2. With N=3 reuse, each co-channel cell is separated by three cell radii, which create enough additional path loss that co-channel interference is minimized. Because a single AP can handle only a finite number of simultaneous users (e.g., 100) and a finite amount of traffic, such a network also maximizes the number of users per square kilometer.

One principle of traffic engineering applies to both circuit-switched and packet-switched networks: All users should share one set of channels (circuit-switched) or one medium (packet-switched) for the most efficient use of the available bandwidth. IEEE 802.11 networks are no exception. A network coordination function minimizes collisions between users on the same network, but harmful interference and low throughput result when two separate networks operate in the same area on the same frequencies.

Another example is 4.9 GHz networks. In the 4.9 GHz band, the FCC authorizes channel bandwidths of 1, 5, 10 and 20 MHz. Existing IEEE 802.11 standards specify channel bandwidths of 10 and 20 MHz, but some vendors also offer 5 MHz channels. The most common channel bandwidth used at 4.9 GHz is 20 MHz because it allows the use of the 802.11a protocol and offers the highest maximum bit rate of 54 Mb/s.

Unfortunately, there is only 50 MHz authorized in the 4.9 GHz band, so there are only two and one half 20 MHz channels. This limitation creates a problem if each agency in a metropolitan area wants its own radio channel — there simply aren’t enough channels. A better approach is to operate one metropolitan-wide network using 10 MHz channels. The 10 MHz channel will allow an N=3 reuse pattern with two channels left over for contingencies or the occasional point-to-point link. The 10 MHz channel results in a 3 dB improvement in sensitivity compared with the 20 MHz channel, and it is more robust in the presence of multipath-induced delay spread. The only drawback to the 10 MHz channel is that the maximum bit rate is cut in half.


Jay Jacobsmeyer is president of Pericle Communications Co., a consulting engineering firm in Colorado Springs, Colo. He holds BS and MS degrees in electrical engineering from Virginia Tech and Cornell University, respectively, and has more than 25 years of experience as a radio frequency engineer.

Tags: Wireless Networks

Most Recent


  • Germany proposes strict curbs on Huawei
    Relying on a Russian thug for energy supplies no longer appeared very sensible to Germany’s government after Vladimir Putin sent Russian troops into Ukraine. Similar dependence by Germany’s telcos on Huawei has looked just as risky to opponents of the Chinese equipment vendor. If Putin could turn off the Nordstream gas taps in response to […]
  • AT&T, Nextivity announce new generation of FirstNet HPUE offerings that include Wi-Fi connectivity
    AT&T recently announced the second generation of FirstNet MegaRange offerings, which uses high-power user equipment (HPUE) technology from Nextivity to effectively double the range of 700 MHz Band 14 signals while being more affordable by supporting device access via Wi-Fi. Matt Walsh–assistant vice president of product management, development and sales for FirstNet, Built by AT&T—said […]
  • Audi, Navistar show how connected-car tech makes bus stops safer
    Audi and Navistar have demonstrated the life-saving potential of connected car technology for millions of American schoolchildren. In a showcase at Herndon, Virginia, the pair – who announced a partnership last year – illustrated how C-V2X (Cellular Vehicle to Everything) tech can prevent accidents by allowing the automaker’s cars and Navistar IC school buses to send messages […]
  • Cradlepoint emphasizes device-level security in latest NetCloud Exchange offerings
    Best known for its versatile in-vehicle routers used by public safety, Cradlepoint is leveraging its recent acquisition of Ericom to enhance its NetCloud Exchange offering by delivering flexible, device-level security services through the platform that follow zero-trust principles, according to company officials. Jonathan Fischer, Cradlepoint’s vice president of business development, said this type of security […]

Leave a comment Cancel reply

To leave a comment login with your Urgent Comms account:

Log in with your Urgent Comms account

Or alternatively provide your name, email address below:

Your email address will not be published. Required fields are marked *

Related Content

  • The battle over connected cars drags on
  • UK officials revamp ESN plans again, target Airwave-to-LTE transition for end of 2026
  • PSCR: Dereck Orr highlights features of June 21-24 virtual event
  • FirstNet buildout on pace for March 2023 completion, AT&T official says

Commentary


Better technology can help solve the public-safety staffing crisis

26th June 2023

Updated: How ‘sidelink’ peer-to-peer communications can enhance public-safety operations

  • 1
27th February 2023

NG911 needed to secure our communities and nation

24th February 2023
view all

Events


UC Ezines


IWCE 2019 Wrap Up

13th May 2019
view all

Twitter


Newsletter

Sign up for UrgentComm’s newsletters to receive regular news and information updates about Communications and Technology.

Expert Commentary

Learn from experts about the latest technology in automation, machine-learning, big data and cybersecurity.

Business Media

Find the latest videos and media from the market leaders.

Media Kit and Advertising

Want to reach our digital and print audiences? Learn more here.

DISCOVER MORE FROM INFORMA TECH

  • American City & County
  • IWCE
  • Light Reading
  • IOT World Today
  • Mission Critical Technologies
  • TU-Auto

WORKING WITH US

  • About Us
  • Contact Us
  • Events
  • Careers

FOLLOW Urgent Comms ON SOCIAL

  • Privacy
  • CCPA: “Do Not Sell My Data”
  • Cookie Policy
  • Terms
Copyright © 2023 Informa PLC. Informa PLC is registered in England and Wales with company number 8860726 whose registered and Head office is 5 Howick Place, London, SW1P 1WG.