LTE UE Device for Cat M: Challenges and Opportunities

These are interesting times in the wireless communication industry. On one front, the explosive growth of wireless communications with its unbelievable data rates is primarily due to the phenomenal growth of cellular users around the world. The cell phone users globally account for hundreds of billions units and yet the handheld phone market segment is continually growing with great demand for one-stop communication applications like Voice-over Internet Protocol (VoIP), video and web-traffic. The internet of things is now getting re-coined as Internet of Everything (IoE) wherein not just human beings, but machine to machine communication through internet would cause another explosion in data traffic. Among the technologies, the 3GPP led LTE (long term evolution), aims to provide higher data rates, low latency, and greater spectral efficiency with technologies like massive MiMo, Carrier Aggregation. On other hand, the newer 3GPP releases namely Release-13, Release-14 and beyond is also geared towards Cat M, Cat-NB devices for Internet of Everything (IoE) market which are primarily in narrow bandwidth range and uses much slower data rates for smaller power, reduced cost requirements. While this rate of growth presents many challenges, it comes with opportunities to tap into newer markets.
This article contributed by T.R Narahari, VP Engineering at Mymowireless, attempts to give the overview of the challenges and opportunities for Mymowireless in the Cat M market .The Cat M User devices are at a nascent stage. However several companies have started to offer devices/chipset to tap this emerging market.
Key requirements for Cat M
Low cost: About 60% device cost reduction can be achieved by a variety of techniques like Implementing the recommendations of TR 36.888 low cost study reports and other techniques for reducing cost. A representative list is given below.

  • Reduced Bandwidth to 1.4 MHz for Cat M; Reduced bandwidth for both RF and baseband in Downlink, and Reduced bandwidth for both RF and baseband in Uplink.
  • Single antenna.
  • Half duplex FDD operation.
  • Reduced peak rates; by reduction of maximum transport block sizes for DL and UL, Restricting the number of PRBs in an assignment/grant, and Restricting the maximum modulation order.
  • Reduced Transmit Power.
  • Reduced memory requirements.

Long Battery life typically to achieve >10 years. This can be achived by mainly considering two attributes. One is Power Saving Mode (PSM): Device remains registered on network despite being unreachable thus reducing the signaling needed to wake up. Other is Extended DRX: Extended Sleep cycles in idle mode, avoid unnecessary receiver activations.
Wide Spectrum: The spectrum is optimized for IoT diversity.
Support of device volume: Total number of M2M devices could be orders of magnitude greater than traditional devices.
Extended Coverage (7X): Additional +20dB achieved by repetition of transmission , new control channels and new access procedures.
Complexity Reduction
It is estimated that the complexity of Cat M device would be 50% less than the complexity and risk that comes from the fact that development of Cat M device has to meet the demand of data rates while still being attractive on cost, power, area and last but not least performance. The device has to be configurable/programmable for both PHY and L2L3 processing and this can be achieved better with a software solution that is regularly updated. For example, a protocol feature like OTDOA could be added in software easily than in hardware late in the development cycle, thus giving flexibility.
The architecture and partitioning needs to take into account the Configurability, Low Power, and Low Cost. Having separate L2L3 processing block and separate PHY processing block allows better configurability. Implementation of UPF based independent power domains for ON/OFF as well as architectural techniques like E DRX, PSM can leverage the low power requirement. Implementing the select recommendations of TR 36.888 results in low cost according to study reports.
Mymowireless Success
Mymowireless founded by Dr Sondur Lakshmipathi in 2008 is uniquely positioned to tap into both the opportunities. On the first front, Mymowireless has a reference modem solution which supports Cat1 to Cat 4. Mymowireless licensed the UE Solutions to chip companies in USA and to other customers worldwide. Subsequently, the chipsets and prototype UE modems have passed GCF tests in USA major carrier labs.
This article attempted to give a high level picture of the emerging technology trends in wireless space on both at the high end of performance and at the low end of cost and power requirements. The requirements that are to be satisfied to bring down the cost of the Cat M LTE device down is brought out from Mymowireless perspective who already have a Cat 4 and Cat 1 LTE UE reference device which has passed GCF tests.
T.R Narahari, VP Engineering, Mymowireless
T.R. Narahari has over 25+ years of industry experience specializing in Embedded and VLSI domains. He was Senior Engineering manager at LSI Logic India Pvt ltd during 2013-2014. He worked in Intel India during 2004 -2009 as Engineering Manager & has worked in MNCs like Open-Silicon, Wipro and Real Chip. He worked in Dept of Space as Scientist D during 1991-1998. At Mymowireless he focuses on LTE IPs, Strategy, and Business development. Narahari completed his masters in Digital electronics from CUSAT in 1991 and B.E (ECE) from Osmania University in 1989.

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