Moving from LMR P25 towards LTE: can your current microwave backhaul get you there?

By James Rugg

As with all technology innovations and advancements within an industry, the process of upgrading and migrating is complex and involves multiple factors for consideration. This abstract by Jim Rugg, the Director of Public Safety and Federal Markets at Ceragon Networks, offers insight into essential factors for Public Safety (PS) communication officials to consider when migrating from Land Mobile Radio (LMR) P25 to LTE infrastructures, with a focus on the importance of microwave backhaul networks.

To further understand this recent shift, it's important to determine the underlining drivers that are pushing for this change. When it was announced several years ago that a national public safety broadband network would be built in the United States to support first responders, the mission critical communications industry divided into 2 main camps.

One camp was (and mostly still is) deeply rooted in legacy mission critical systems, which primarily support voice applications in the form of LMR. Despite technology advancements and the expense of building, supporting, and maintaining those systems without consideration for data, this camp is still the main go-to for mission critical voice communications.

The other camp emphasizes embracing technology advancements to improve situational awareness for first responders that have relied on and trusted their mission critical LMR for decades. This group sees LTE as the future for mission critical networks as it can support BOTH voice and data applications.

The challenge is that as of now, LTE has primarily been deployed in support of commercial carrier networks, and has yet to be deployed in support of mission critical networks on a large scale. To drive LTE acceptance, several broadband technology opportunity program (BTOP) grants were awarded in the US to help start planning, building, and maintaining mission critical LTE networks, with the goal of proving that LTE can support the mission.

Most recently, AT&T won the public bid to build the nation's first public safety broadband network without using LMR P25. However, this is a long-term process and during the first several years, only mission critical data will be supported as the 3rd Generation Partnership Project (3GPP) standards group has not yet ratified all requirements to support mission critical voice on LTE networks. However, this has not stopped the promotion of push to talk over cellular (PTToC) by companies like AT&T and several others, that want to see the use of LMR P25 discontinued.

So, how should you plan, build, and maintain your mission critical backhaul networks in the future?

First, find a technology partner who understands your short-term and long-term capital expenditure (CAPEX) plans and operational expenditure (OPEX) challenges in relation to your mission critical microwave transport infrastructure. Whether or not you continue investing in your legacy LMR P25, or whether you are moving toward an LTE infrastructure, selecting the right partner will pay big dividends as you plan a migration.

PS communications leaders often convey that they have limited knowledge of their microwave network infrastructure. It is particularly important to understand that all scenarios require an all Internet Protocol (IP) based transport, regardless of whether you are moving toward LTE or upgrading to LMR P25 Phase II. Even with the push to IP, many agencies still have TDM applications running that require support in their transport infrastructure.

This is where having a long-range plan helps to protect the investments of today when upgrading the microwave backhaul within a mission critical infrastructure.

Here is a list of questions that consulting agencies and communications officials should ask their microwave backhaul solutions providers:

  1. Can the solution support both TDM traffic today and all IP traffic in the near future?
  2. Is native TDM necessary and/or ideal? Or, can the buffering offered accommodate any potential latency impacting TDM applications?
  3. Is advanced buffering and hierarchal quality of service (H-QoS) part of the radios offered in support of legacy TDM?
  4. How many modulation steps do the radios step through when deploying advance code modulation (ACM). ** This is an important question as it relates to level of traffic that can pass in less than optimal

The following are some additional factors to consider:

  • When designing for rain fade margins when a system has a limited number of modulation steps and environmental conditions can change, a link may drop from 256 QAM to BPSK with no levels in between, which significantly reduces available bandwidth.
  • To provide greater available bandwidth in less than optimal conditions, consider a microwave solutions provider that can accommodate multiple steps such as a 1024 QAM to 512 QAM to 256 QAM to 128 QAM, down to BPSK.

Ceragon rises to the challenge of MW design consultants tasked with designing the next generation mission-critical MW networks with our IP-20 assured family of products. All Ceragon IP-20 radios offer a simple, easy-to-use, common interface with additional features that are added to solve the most complex design challenges our customers face.

Ceragon can help you determine if your microwave backhaul can support LMR today and be LTE-ready for tomorrow, assist you in solving MW backhaul design challenges, and ensure peace of mind by making backhaul simple and secure.

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* Must have Microwave links in the network today

* For Public Sector customers only