Overview: This document describes the basic units of the OptiX RTN equipment, and describes how to set up a hop of a microwave link and the problems that occur during the setup. It is intended for beginners. As this is also the first time for me to learn about microwave and related products, please leave a message if you have a wrong understanding.
Networking Structure
This document describes the simplest hop of the microwave link. The following figure shows the networking.
In the lab, no antenna is available. Therefore, an RF cable is required to connect the ODUs at both ends. To simulate the fading that occurs during the air interface transmission on the live network, a fixed attenuator or a variable attenuator is required when the RF cables are connected to the ODUs at both ends. The fixed attenuator is used to fix the attenuation value, and the variable attenuator is used to adjust the attenuation value.
As shown in the preceding figure, the system consists of the IDU, ODU, and antenna. The IDU is referred to as an indoor unit, and the ODU is referred to as an outdoor unit. The IDU performs multiplexing, coding, modulation, and D/A conversion of service signals into IF analog signals. The ODU converts the IF analog signals transmitted by the IDU into RF signals through frequency conversion and power amplification. The antenna performs conversion between RF signals and electromagnetic waves and transmits and receives signals in space.
The IDU consists of the interface unit, timeslot unit, packet switching unit, IF unit, power unit, fan unit, clock unit, and control unit. The IF unit converts service signals and analog signals into each other.
IF unit
The following figure shows the structure of the IF unit.
Logic processing unit: receives VC-4 signals and pointers transmitted by the timeslot unit, and processes clocks.
Ethernet processing unit: receives Ethernet signals from the packet switching unit.
Multiplexing unit: demultiplexes VC-4s into E1s for E1 services. For STM-1 services, add pointers to VC-4 signals and multiplex overheads into STM-1 signals. Adds microwave frame overheads to E1/STM-1 service signals to form microwave frame signals. In addition, the receive direction parses and checks the fields (such as ATPC, link ID, and check code) in the overheads of microwave frames, and reports the corresponding alarms and performance events.
Modem unit: performs digital modulation (loads service signals to carriers) and FEC coding.IF processing unit: performs digital-to-analog (D/A) conversion, analog modulation, and filtering.
Combiner interface unit: Combines ODU control signals, service signals, and power signals to form IF analog signals, and then transmits the IF analog signals to the IF cable.
Setting Up a Hop of microwave link
The process of setting up a hop of the microwave link is divided into three steps: physical cable connection, NE configuration, observation, and commissioning.
Physical Cable Connection
According to the networking structure, two IDUs (including the IF board and SCC board) and two ODUs (high and low sites with the same frequency) are required. In addition, IF cables, fixed attenuators or tunable attenuators, waveguide connectors, and RF cables are required. The detailed cable connection process is not described here.
Configuring NEs
After connecting the cables, you need to configure the NEs at both ends. The configuration is performed through the CLI. The configuration consists of the IF configuration of the IDU and the RF configuration of the ODU.
ODU RF configuration:
1. Check the ODU information. Ensure that the ODU frequencies at both ends are the same. Check the T/R spacing and a maximum bandwidth of the ODUs. The command line is: radio-cfg-get-odu-info.
2. Set the T/R spacing between the ODUs at the two ends, that is, the frequency spacing between the Tx high station and Tx low station. The high station refers to the end where the to transmit frequency is greater than the receive frequency. The command line is radio-cfg-set-odu-trspacing.
3. Configure the transmit frequencies of the ODUs at both ends. Ensure that the transmit frequency at the local end is the same as the receive frequency at the peer end. The command line is radio-cfg-set-odu-txfreq.
Note: You can run the radio-cfg-get-odu-rfreq command to query the actual transmit and receive frequencies of the ODU.
4. Configure the transmit power of the ODUs at both ends. Ensure that the transmit power is within the configurable range. Run the radio-cfg-get-odu-tsl-rg command to check the transmit power. In addition, different modulation schemes support different modulation ranges. You can run the radio-cfg-get-am-odu-txpower-rg command to view the supported modulation ranges. Note that the transmit power at the local end cannot be too low. If the transmit power is too low, the RSL at the opposite end may be lower than the sensitivity. For details about the sensitivity of each modulation mode, see the related Excel specification table. In this case, the link is unavailable. Run the radio-cfg-set-odu-tsl command to configure the transmit power.
IF configuration of the IDU:
Configure the IF working modes of the IDUs at both ends (different IF boards support different IF working modes), and ensure that the IF working modes at both ends are the same. The command is radio-cfg-set-if-runningmode.
Run the radio-cfg-set-bandwidth command to configure the bandwidth for the IF boards at the two ends. The bandwidth cannot exceed the maximum bandwidth supported by the ODU. (You can view the maximum bandwidth in the ODU information.)
Configure the same modulation scheme for the IF boards at both ends. In addition, the AM enabling status must be the same as the AM enabling status. The command line is radio-cfg-set-acm-param.
The basic configuration is complete. You can check whether the link is normal by viewing the alarms and MSE.
Observation and commissioning
Check whether the link is available by running the alm-get-curdata-ext command. If the MW_LOF alarm does not exist, MW_BER_EXC alarm. Check whether the MSE value is radio-cfg-get-mse (the value is 0 when the link is unavailable and is greater than 400 when the link quality is good). In addition, insert services and use a meter to check whether data is received normally and whether packet loss occurs.
After the preceding steps are performed, the MW_LOF alarm is reported and the MSE value is 0, indicating that the link is unavailable. The process of locating the fault is as follows:
Check for other alarms, such as CONFIG_NOSUPPORT or MW_CFG_MISMATCH. After checking, Huawei found that the CONFIG_NOSUPPORT alarm was reported. According to the para, the ODU module was faulty (0X3) and the transmit power was incorrectly configured. The cause is that the transmit power of the ODU is not configured.
After the transmit power is configured, the MW_LOF alarm persists. Checked the IF working modes (IS8), channel bandwidths (56 Mbit/s), and modulation modes (AM disabled and 64QAM) at the two ends. The IF working modes, channel bandwidths, and modulation modes at the two ends were consistent. The receive and transmit frequencies of the ODUs at the two ends were inconsistent. The principle is to ensure that the transmit frequency at the local end is the same as the receive frequency at the peer end, and the receive frequency at the local end is the same as the transmit frequency at the peer end. Therefore, change the transmit frequencies at both ends.
After the two problems are solved, the MW_LOF alarm is cleared and the MSE becomes normal. Then, the MW_CFG_MISMATCH alarm is reported on the equipment. According to the para, the IF board is faulty (0X1). It is found that the number of E1 timeslots at the two ends is different. Set the same number of E1s at both ends based on the radio-cfg-set-e1capacity. The MW_CFG_MISMATCH alarm is cleared.
Conclusion: When the link is disconnected, you can view the alarm, find the incorrect alarm, and check the related document to find the faulty board and the cause.
Thanks for reading.
