Introduction to Long Term Evolution (LTE) Technology - Scott Johnston Comcast West Division

Introduction to Long Term
Evolution (LTE) Technology

            Scott Johnston
            Comcast West Division

       2013 NW Tech Days and Vendor Show

Discussion Topics

    1.   Wireless Telephony – A Brief History
    2.   Theory Of Operation – Technical Information
    3.   Introduction To OFDM
    4.   Understanding LTE’s Affect On Our Networks
    5.   High Frequency Ingress And Egress
    6.   Our Affect On LTE Networks
    7.   Troubleshooting LTE interference

2

A Brief History

3

The Cellular Age

    1973 – Motorola produces first production handheld telephone – 30
    minutes of talk time, 10 hours to charge – Dr. Martin Cooper claims
    his vision was inspired by Captain Kirk’s communicator on Star Trek
    1978 – 1G – first generation known as Advanced Mobile Phone
    System (AMPS) launches in America - the service is analog,
    insecure, and can be cloned
    1990 – 2G emerges – CDMA is in use in the United States – SMS
    text messaging becomes widely available – uses circuit switching
    2001 – 3G Networks commercially deploy first by Monet Mobile
    Networks and then by Verizon Wireless – packet switching
    (connectionless) technology
    2007 – 295 million subscribers on 3G networks worldwide
    2008 – US Government auctions off the 700 MHz band – AT&T and
    Verizon win the majority of the spectrum

4

Internet Connectivity and LTE

    2009 – 3G technology is used in MiFi style mobile Internet devices
    2010 – 4G service launches in America
    2013 – LTE Advanced launches in UK – twice as fast as current 4G
    and ten times faster than standard 3G networks -
    2013 – 91% of Americans own a cell phone
    Future – Plans include further bandwidth auction allowing LTE
    providers to operate down into the 500 MHz range

5

LTE - Technical Information

    •   LTE Goals – to increase the capacity and speed of wireless
        networks using modern modulation schemes and Internet
        Protocol to reduce latency found in previous cellular standards
    •   LTE Band – 4G networks operate outside of 2G and 3G
        bandwidth – Currently 698-806 MHz (CATV channels 109-123)
    •   LTE Bandwidth – Currently 300Mbits down / 75Mbits up
    •   LTE Downstream uses Orthogonal Frequency Division
        Multiplexing – essentially employing QPSK, 16QAM and 64QAM
        at once
    •   LTE Upstream uses Frequency Division Multiple Access (FDMA)
        where frequency slots are granted to users on QPSK or 16QAM
        channels
    •   Fun Fact – LTE cannot operate when the handset is moving
        faster than 220 MPH

6

Introduction to OFDM

    •   Orthogonal Frequency Division Multiplexing – an advanced
        modulation method capable of delivering more bandwidth with
        less errors
    •   Traditional modulation methods use single carriers to carry
        encoded data

    •   OFDM uses the available spectrum more efficiently transmitting
        many single carriers together

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Introduction to OFDM (cont…)
    •   Imagine multiple QAMs being transmitted at once “on top” of each
        other

    •   High speed wireless N routers have been using this technology
        for several years - also known as MIMO (multiple in multiple out)
    •   DOCSIS 3.1 will rely on Orthogonal Frequency Division
        Multiplexing to increase capacity compared to traditional channel
        bonding – up to 10Gbps/1Gbps
8

LTE’s Affect On Our Networks
    •   Off-air LTE interference can impact downstream performance in
        several frequency ranges
         • Verizon uses 746-756 MHz for downlink, 777-787 MHz for
           uplink
         • AT&T uses 734-746 MHz for downlink, 704-716 MHz for uplink

    •   Ingress affected CATV channels
         • 109-111, 114-118, 121-123

    •   The effects of LTE ingress can vary based on several factors
         • Distance from LTE cell towers
         • Atmospheric conditions – RF travels farther in the air at night
         • Downlink or Uplink interference? – from the phone or tower?
         • LTE network utilization and OFDM signal power distribution
         • In-home wiring issues in close proximity to LTE use
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High Frequency Ingress And Egress
     •   Cable is intended to be a closed system however we know off-air
         ingress is a continuous issue in our outside plant and the
         customer premise
          • Often times if there is signal ingress there is also some sort of
             egress
     •   There is a large disconnect between low frequency FCC
         compliance leakage detection and high frequency LTE band
         interference
          • Much of our FCC compliance leakage can be found in the
             customer premise
          • New data provided by Arcom shows that much of the LTE
             band egress comes directly from the cable plant and cannot be
             detected with a standard U/VHF band leakage detector

                    Image courtesy of Arcom Digital
10

High Frequency Ingress And Egress
                 •   In this photo example you can see the
                     FCC U/VHF band Sniffer Sleuth
                     reading 8uV/Meter

                 •   The Arcom Snare is detecting a
                     5500uV/M digital leak in the LTE band

                 •   LTE providers have a keen interest in
                     protecting their frequency bands and
                     have been known to contact cable
                     operators to advise them of LTE band
                     signal leakage

11

Our Affect on LTE Networks
     •   High frequency RF energy can affect LTE cell sites and
         customers near the point of egress

     •   Often times the RF being radiated by our plant is high-level since
         we tilt the outputs of our amplifiers

     •   Unless we are actively monitoring with high frequency digital
         leakage gear we may be totally unaware of the problem we are
         causing for LTE operators

     •   LTE operators have equipment to determine the source of our
         leaks and are ready and willing to advise us of our problems if
         and when our leakage affects LTE services

     •   If LTE band signal leakage is affecting LTE operators the problem
         causing it is most likely affecting our customers too!
12

Troubleshooting LTE Interference
     •   Traditional troubleshooting methods we’re already familiar with
         work here
          • Divide and conquer method
          • Test drop
          • FCC signal leakage detection – not always effective
          • MER/BER/Constellation measurements in known off-air
            ingress bands (~698-806 MHz)
          • Handheld spectrum analyzer detection

     •   There are more advanced methods available as well
          • Arcom QAM Snare Digital Leakage handheld
             • The Snare is a complete solution that essentially samples
                the forward coming out of the head-end while the
                “Navigator” in the vehicle looks for the head-end sample
          • Trilithic Seeker D – truck mounted high-frequency digital
            leakage gear – integrates into existing LAW platform
13

Troubleshooting LTE Interference
     •   Rohde & Schwarz handheld analyzer
          • High-end spectrum analyzer – manual detection with external
            antenna – best when LTE operators report known signal
            leakage to the MSO

     •   Full Band Capture tools
          • Broadcom’s BCM3383 chipset contains a full 1GHz spectrum
            analyzer
          • MSO’s are busy writing software to decode FBC chipsets
              • Comcast has Spectra
              • Other MSO’s are not far behind
          • These software applications will undoubtedly become
            automated to some degree in the future leading us closer to
            affected areas

14

Questions?

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