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Telecom Network And Network Testing

Madhukar-Tripathi
Madhukar Tripathi, Head – MARCOM &OPTICAL PRODUCTS, ANRITSU INDIA PVT.LTD

Test and Measurement: Network Test Network testing is very broad subject. In this article I am covering telecom (mobile) network testing. Telecom network can be divided into 2 major category- wired network and wireless network from installation and operation point of view. Telecom network is hybrid (combination of Wired and wireless network). Wired and Wireless network are essential and important part of all telecom network. Due to 5G network deployment worldwide this article covers network testing having 5G network as focus.

wired network measurement
Figure -1: 5G Mobile Network

CU- Central Unit
DU- Distributed Unit
RU- Remote Unit
eCPRI- Ethernet Common Public Radio Interface
RoE- Radio Over Ethernet
MEC Mobile Edge Computing
GM/GMC- Grand Master Clock

Transport Measurements required by 5G Mobile Network I&M (Installation and Maintenance) contain following measurements:

  • 5G Mobile Network eCPRI/RoE Measurements
  • 5G Mobile Network Latency Measurements
  • 5G Mobile Network Time Synchronization Measurements

5G Mobile Network eCPRI/RoE Measurements

Common Public Radio Interface (CPRI) compliant interface equipment has been used for 3G and LTE systems to convert the mobile fronthaul wireless signal to the optical signal. CPRI is commonly said to need to be about 16 times faster than the radio transmission speed to perform digital conversion of radio signals. Since 5G transmission speeds are about 100 times faster than LTE, a new eCPRI/RoE technology based on market mainstream Ethernet is being adopted. With 5G featuring high speeds and large capacity, maintaining mobile fronthaul communications quality requires communications and latency tests measuring either CPRI or RoE frame bit errors and latency with high accuracy.

The 1914.3 (RoE) and eCPRI frame formats both use Ethernet in their lower layers, allowing timing areas to be tested using standard Ethernet timing methods. Areas such as latency, routing, switchover time, and BER over the 1914.3 and eCPRI frame formats must also be tested.

5G Mobile Network Latency Measurements

Since maintaining minimum assured communication speeds is generally impossible using Ethernet, latency times of the entire network including the 5G mobile fronthaul must be managed strictly. To suppress latency times between the mobile fronthaul 5G antenna and Core/Metro network, it is important to minimize the latency of the network equipment as much as possible. Implementing the 5G low-latency feature requires using two testers to accurately measure one-way delay between two distant separate points.

eCPRI standardsBoth the 1914.1 and eCPRI standards require a known network latency, ensuring delivery of the frame payload to the RF interface accurately and reliably. Different standards offer insight into network latency requirements; 3GPP discusses how latency from the BBU to UE and back RTT must be within 1 ms for URLLC, while IEEE 802.1CM requires a latency of 100 µs across the transport network between the CU and RU. IEEE 1914.1 focuses on the area of the transport network, offering more in-depth details, splitting it into sub-classes based on network segments and traffic types.

5G Mobile Network Time Synchronization Measurements

At present, time synchronization between base stations commonly uses GPS time data, but this method is limited by the ability of GPS radio waves to reach some locations where base stations are installed, such as inside buildings and underground shopping malls, etc. To remedy this problem, PTP-based time synchronization is being deployed at some locations. Since PTP is unaffected by installation location, it is being proposed for 5G, making it more important than previously Use of the 5G mmWave band requires many small base stations because the high radio-wave frequency only propagates over short distances. As a result, the Precision Time Protocol (PTP) is used to synchronize time between base stations. Time synchronization using PTP demands strict evaluation of the entire network to maintain time differences within the permissible range.

gpsMobile fronthaul test include:

  • eCPRI/IEEE1914.3 Frame test and high-resolution Latency test
  • CPRI/OBSAI L1 test
  • CPRI/OBSAI L2 test
  • Pass-through monitoring
  • CPRI over OTN

CPRI/OBSAI measurements

  • CPRI/OBSAI L1 Test
  • CPRI: 614.4, 1228.8, 2457.6, 3072.0, 4915.2, 6144.0, 9830.4, 10137.6 Mbps 12.1651 Gbps, 24.3302 Gbps
  • OBSAI: 768, 1536, 3072.0, 6144.0 Mbps – Clocks: Internal, External (10 MHz), GPS – Level measurement (dBm) – Bit rate (bps) and deviation (ppm) measurement – Alarm/Error detection (Signal Loss, PSL, Pattern Error) – Unframed BER measurement
  • CPRI L2 Test – Link status monitoring – Alarm/Error detection (Signal Loss, LOS, LOF, R-LOS, R-LOF, RAI, SDI, Reset, PSL, LCV, INVSH, Pattern Error) – Framed BER measurement – RTD Measurement (min, avg., max) • Pass-through monitoring
  • CPRI over OTN – OTN Alarm/Error detection – L1 Unframed BER measurement using CPRI client signals • Fiber end face inspection using VIP (Video Inspection Probe)

CPRI over OTN Several vendors are working on CPRI over Optical Transport Network (OTN) solutions supporting transport of the raw radio (CPRI) data from the RE over optical fiber to a centralized location for baseband processing.

  • A single location can serve multiple REs.
  • This level of consolidation has huge power and cost savings over the distributed approach without impacting network scalability. OTN supports transport of several protocols over the same fiber, offering OTN operators fault management, performance monitoring, and protection mechanisms coupled with low cost-of-entry and the ability to support current, future, and legacy infrastructure technologies. OTN operators also enjoy the advantage of using the same network-wide management system.

Mobile backhaul test include:

  • Test and analysis of Synchronous Ethernet and PTP:

o SyncE (ITU-T G.826x) o PTP (IEEE 1588 v2)
o G.8265.1, G.8275.1 and G.8275.2 telecom profiles
o Time/Phase error measurement. (with High Performance GPS Disciplined Oscillator MU100090A)

  • Synchronous Ethernet run together with normal Ethernet functions including: o Ethernet tests at 25 Gbps, 10 Gbps, 1 Gbps, 100 Mbps and 10 Mbps o Ethernet Service Activation Test (Y.1564)

o Automated RFC 2544 tests of Throughput, Frame Loss, Latency or Packet Jitter and Burstability
o BER tests – include Frame Loss and Sequence Error tests
o Service disruption measurements

Ethernet test include:

  • Ethernet tests at 100 Gbps, 40 Gbps, 25 Gbps, 10 Gbps, 1 Gbps, 100 Mbps and 10 Mbps
  • Traffic generation up to full line rate
  • IPv4 and IPv6 test
  • Ethernet Service Activation Test (Y.1564)
  • Industry defined IEEE, IETF and ITU-T benchmark testing
  • TCP Throughput option (RFC 6349)
  • BER tests – include Frame Loss and Sequence Error tests
  • Service disruption measurements
  • Ethernet OAM tests
  • 10G WAN-PHY tests
  • Synchronous Ethernet test (ITU-T G.826x and IEEE 1588 v2)
  • Ethernet Multistream • Stacked VLAN (Q-in-Q)
  • MPLS tests
  • MPLS-TP and PBB/PBB-TE tests
  • Ping • Traceroute
  • Frame capture for protocol analysis with Wireshark
  • Electrical cable tests and optical signal level test

SyncE (Synchronous Ethernet)

Regular Ethernet is an asynchronous communications standard where the timing of data sent and data received are not matched. This simplifies the type of transmission equipment needed. Smartphones, however, require synchronized timing of data between base stations in order to permit uninterrupted transmission as the Smartphones move between base stations. The ITU-T organization has established a new standard called SyncE that adds a function for synchronizing asynchronous Ethernet communications. In addition, IEEE also has a new standard known as IEEE 1588 v2 for matching times.

Anritsu’s Ethernet test solution supports standard Ethernet communications and is also the ideal platform for verifying, developing and troubleshooting the new SyncE (Synchronous Ethernet) and IEEE 1588 v2 functions used by base stations.

anritsuAnritsu Network Master Pro MT1000A is ideal test platform to support all legacy wired network and latest 5G network supporting backward compatible 3G and 4G network. SEEK is a automation, one button feature which helps engineers to test network in less time, accurately.

Wireless Measurement using Field Master Pro MS2090A Wireless measurements are performed at various stages-right from network planning to deployment and operation to network maintenance.

Due to 5G technology focus most of operators are planning 5G network or will roll out 5G network soon. Much of the world is focusing initial 5G rollouts on the 3GPP defined FR1 bands (those carriers with frequencies below 6 GHz). South Korea Japan, China, USA , Germany etc rolled out 5G network. Note: 5G technology Spectrum is divided into 2 parts- FR1 and FR2.

FR1- Sub 6Ghz band / frequencies.
FR2 –millimeter-wave (mmWave) – frequencies.

There are practical differences between FR1 and FR2 signals. There are also technological differences that will impact performance and testing. Per the 3GPP standard, mmWave 5G NR signals have subcarrier spacing of either 120 or 240 kHz, compared to only 30 or 60 kHz for FR1. This results in a wider sync signal block (SSB) – 28.8 and 57.6 MHz, respectively. The SSB contains the SSS, PSS, and PBCH information, which are required for demodulation and signal identification. Therefore, any instrument or device must have the capability of capturing wide bandwidths of data (at least as wide as the SSB) in order to make proper ID of and communication with the radio. FR2 signals also have more SSB beams.

All 5G NR base stations transmit SSB beams through the antenna’s transmission sector, but mmWave radios use between 12 and 64 beams, whereas FR1 radios are limited to 4 or 8 beams. With 64 beams, the radio can transmit narrower beams with more power, which improves the efficiency of the radio and helps avoid interference. However, more beams require decoding more bits from the PBCH in order to read out all 64 beam indexes in their correct position. It also requires a greater number of antenna elements in the antenna array used for beam forming. This makes it impossible to do connected testing and verification of the radios, forcing users to do all testing OTA.

Finally, mmWave signals have shorter wavelengths (as hinted in the name), which will cause greater propagation loss through both air and most physical objects – including windows, which are often coated with UV protective films which strongly attenuate mmWave RF. This means 5G mmWave service will require greater radio density and strategic placement/ alignment. It will also make signals more vulnerable to interference and requires test equipment with lower noise floors and faster sweep speeds in the mmWave bands.

Testing 5G NR mmWave

Spectrum clearance, interference test is carried during network planning stage after spectrum allocation. Once spectrum is cleaned, scanned for allocated frequency, network planning, sites are decided.

Testing 5GInstallation Verification

  • Once spectrum is clear and radios are going up, it will be key to ensure the radios are configured correctly and performing per standard. – validate the performance of the gNB base station with essential measurements that are in full compliance with 3GPP TS 38.104 V15, including i.e. The Field Master Pro MS2090A offers a full 5G NR demodulation suite, which decodes the SSB beams to provide the following information:
  • Cell ID, Sector ID, and Cell Group
  • Frequency error
  • Time offset
  • Individual beam RSRP, RSRQ, and SINR
  • EVM of the individual SSB parts
  • Multi cell measurements
  • Channel power / occupied bandwidth

Single Cell TestingSingle Cell Testing

ID information is important for verifying the configuration of the radios. Network operators rely on proper radio identification to pinpoint issues with service, interference, or gaps in coverage. Cells are usually hung in groups of three, each covering one of three sectors. The cell ID is then equal to 3 x CELL GROUP + SECTOR ID

Frequency error is key to performance, where less error promotes greater signal quality and faster throughputs. According to the 3GPP standard for 5G NR OTA testing (TS 38.104, section 6.5.1.2), the base station frequency error should comply to standards as follows:

frequencyTime offset is key to full network performance. All 5G NR signals should be tightly synchronized to GPS. Time offset measures the difference between the GPS clock and the start of the frame. This avoids interference between cells. Per the 3GPP standard, the time offset should not exceed 2 µs at a distance less than 1 km.

RSRP, RSRQ, SINR, and EVM are key indicators of radio performance and signal quality. The average EVM of the signals should typically be under 15% with a high quality beam (one with high RSRP and SINR).

Multi Cell The Field Master Pro MS2090A also offers a measurement of multiple radios in the same capture (called Multi Cell in the instrument). By utilizing advanced noise cancellation methods, it is able to read out multiple cell IDs for a single geographic point and show the RSRP of every beam from strongest to weakest. This is powerful for mapping coverage in these dense radio environments. Network planners can utilize the Multi Cell measurement to identify radio handoff points and possible gaps in coverage, even mapping out the coverage, cell by cell.

multi pci scannerPost installation of 5G sites, coverage mapping test is also carried to ensure Base Station (BS) is transmitting to designed / planned area.

5G coverage mapping receive a clear representation of the signal strength of 5G transmitters over intended geographic area by continuously measuring RF data – including 5G channel power, EIRP, or RSRP – with results graphically displayed on a digital map or building floor plan

NEON mapping toolsThe Field Master Pro MS2090A with NEON mapping tools allows users to map out beam powers across a 5G mmWave radio’s full sector

Conclusion: 5G network is evolving and involves more complex methods, hence testing of network & devices are very important part of network life and network performance. Network performance testing reflects customer experience. Network testing will pay in longer term during network deployment and post deployment. Selection of right testing tool is equally important. This ensure efficient network testing and solve issues in timely manner.

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