JOURNAL OF TELECOMMUNICATIONS, VOLUME 26, ISSUE 1, JULY 2014

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Solution for Improving Bit Error Rates (BER) in Microwave Long Haul Links

Ahmed Qaddus, Muhammad Irfan and Aamir Ali Raza

Abstract In the recent years there is a tremendous boost in the demand of triple play applications like voice, data and video in Wireless Telecom sector. For providing triple play applications like voice, data and video to customers the common wireless

backhaul media used by the telecom operators today is Microwave radio links. Microwave radio links are designed on the princi-

ple of point to point wireless architecture. The Microwave radio links are used for transmission of E1s, STM-1 and Ethernet Traf-

fic. Single Microwave radio link in (1+0) configuration can carry data traffic up to 155.5 Mbps which is equivalent to STM-1.

When Microwave radio links are deployed over large ranges then signal to noise ratio (SNR) levels start to degrade, which

causes increase in bit error rates (BER) which result in latency levels above 1 msec, which are not desirable for data transmis-

sion. In this research the Authors have practically implemented solution in field for improving bit error rates (BER) in Microwave

radio links. The real time results for latency measurement are calculated before and after the proposed changes with the help of

JDSU 6000 Generator and Test equipment. The proposed changes focus on antenna alignment and requirement of different

antenna sizes used during Microwave radio link installations on extensive hops.

Index Terms Signal to Noise Ratio (SNR), Bit Error Rates (BER), Latency, Microwave radio link.

1 INTRODUCTION

In order to run high banwidth uniterupted voice, data and video applications over a wireless medium. It is nec-essary to have appropriate signal to noise ratio (SNR) levels above a desire receiver threshold level to avoid latency below 1 msec. Only a wireless link having a low bit error rates (BER) can effectively accommodate high bandwidth uniterupted voice, data and video applica-tions with less than 1 msec delay. In Long haul Micro-wave radio link the main challenges are to establish a wireless link with Low bit error rates (BER) and high sig-nal to noise ratio (SNR) levels.

Authors in this research have practically implemented solution in field for improving bit error rates (BER) in microwave long haul links. By using microwave Point to Point radios in 1+0 Configuration which offer features like N x E1 (8 x E1, 16 x E1, 32 x E1, 64 x E1) in PDH hier-archy, STM-1 in SDH hierarchy, Up to 156 Mbps in Layer 2 Ethernet communication and uses QPSK, 16, 32, 64 and 128 QAM modulation techniques [1].

2 MICRWAVE RADIO COMPONENTS

The terminal structure of the Microwave radio link con-sists of two main parts, which are the Outdoor Unit (ODU) and the Indoor Unit (IDU). A (1+1) Protected ra-

dio terminal consists of 1 fully loaded (height of 2U) IDU and 1 fully loaded (housing two RF transmit-tance/reception modules) ODU. There are 2 co-axial ca-bles bearing the IF mark between the IDU and ODU. An (1+0) unprotected radio terminal consists of 1 partly load-ed (height of 2U) IDU and 1 partly loaded (housing one RF transmittance/reception module) ODU. There is 1 co-axial cable bearing the IF mark between the IDU and ODU. The ODU consists of RF reception/transmittance modules contained within a mechanical box with a wa-terproof design, and Diplexer filters set to its operating frequency band. The special direct mount antenna is di-rectly connected to the ODU, allowing the user ease of installation. Standard antennae are connected to the an-tenna ports on the ODU with the help of twistable-flexible waveguides. The mechanical framework of the ODU al-lows it to be mounted on 3 or 4 inch pipes with the suit-able mounting apparatus. In this way, the unit can be mounted on a tower, on a roof, or a flat surface. It can also be mounted within the building when required. The IDU (Indoor Unit) can be mounted within a standard 19 inch cabin. The IDU uses the same mechanical framework for (1+0) and (1+1). The Microwave radio link uses QAM, QPSK, 16 QAM, 32 QAM, 64 QAM, 128 QAM modulation techniques that allows modification/selection over soft-ware. In this way, efficient and productive utilization of the spectrum is ensured [2]. 3 COMISSIONING TEST After the antenna, ODU, IDU and IF cable has been prop-erly installed and system powered up at both ends, the following tests should be performed on each installed link.

A. Qaddus is working with the R&D Department, NationalRadioTelecom Corporation Haripur Hazara, Pakistan and is aPHD Scholar in Bahria University Islamabad, Pakistan.

M.Irfan is working with the R&D Department, NationalRadioTelecom Corporation Haripur Hazara, Pakistan.

A.Ali Raza is aPHD Scholar in BahriaUniversity Islamabad, Pakistan.

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3.1 Link Verification

1. Verify that Active LED on IF modem card of the IDU front panel is red and stable, indicating the radio link is up. Otherwise the link is not estab-lished and need alignment or the far end is not powered up.

2. The RSSI should be above the threshold level. The chart for various threshold levels is given below in table 1.

3. Radio Bit Error Rate (BER) should be less than or equal to the defined threshold. BER of the order of 10E-6 is standard low BER.

4. If working with ATPC, the RSSI threshold level should be set in safe limits (>= guaranteed thresh-old refer table-1).

5. After connecting test equipment or end equipment to the line interfaces, only active link LED is on the front panel of the IDU panel is ON in red, rest of the LEDs are off.

6. Once link is establish user can see the status for RL1 & RL2 on the web browser and command line interface as shown in snapshot Figure-1 & 2 re-spectively.

7. Please note that any system in the network can be accessed by giving its IP address.

TABLE 1

RSSI THRESHOLD LEVELS

Figure-1 RL Webbased Interface

Figure-2 RL Commandline Interface

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3.2 Line Interfaces/Loopback Test 1. For 2.048Mbps Interface connect PDH test equip-

ment to the E1 interface and verify error-free op-eration for at least 1 hour. Use a physical or soft-ware loop at the far end.

2. For FE/GbE Interface connect a Packet Analyzer to the Fast Ethernet interface and verify error-free operation (no packet loss) for at least 1 hour. Use a physical loop at the far end.

3. For155MbpsInterface connect SDH/SONET/ATM test equipment to the 155 Mbps interface and ver-ify error-free operation for at least 1 hour. Use a physical or software loop at the far end.

3.3 BER for E1

1. Install E1 Mux card in the IDU and verify that it is enabled.

2. Create test environment as shown in figure-3. 3. Configure services according to test requirement. 4. Perform minimum 3-minutes bit error testing on

each E1 port by making hard loop on the desired E1 port on the DDF/Patch Panel.

5. Perform 24-hour bit error test on any one E1 port. 6. Bit Error Rate (BER) should be less than or equal

to the defined threshold (10E-6).

Figure-3 E-1 BER TEST SETUP

3.4 Performance Test for STM1 1. Install STM1 Mux card in the IDU and verify that

it is enabled. 2. Create test environment as shown in figure-4. 3. Configure services according to test requirement. 4. Perform minimum 3-minutes performance testing

on each electrical or optical port of mux card by making hard loop on the electrical / Optical STM1 Port.

5. Perform 24-hour bit error test. 6. The configuration, performance analysis and re-

sults could be stored in a file in most of the test equipments and can be exported to a PC/Laptop. It can also be printed directly by connecting a printer with the test equipment (Ant-5 or MTS-6000). A Performance test was conducted for 18 hours.

Figure-4 STM1 PERFORMANCE TEST

TABLE 2

E1 BER TEST RESULTS

Performance Analysis

(M.2100)

Near End Far End

ES 0 0.00% * *%

EFS 10 100.00% * *%

SES 0 0.00% * *%

UAS 0 0.00% * *%

Verdict Pass *

Path Alloca-tion 100%

Event Log

No. Event Date Start time

Stop time

Dur. / Cout

0 Start 5/4/2013 55:43.0

1 Stop 5/4/2013 55:53.0

TABLE 3

STM1 PERFORMANCE TEST RESULTS

Performance Analysis

(M.2100)

Near End Far End

ES 0 0.00% *

EFS 1800 100.00% *

SES 0 0.00% *

UAS 0 0.00% *

Verdict Pass *

3.4 Delay Test for STM1

1. Install STM1 Mux card in the IDU and verify that it is enabled.

2. Create test environment as shown in figure-4. 3. Configure services according to test requirement.

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4. Perform minimum 3-minutes delay testing on each electrical or optical port of mux card by mak-ing hard loop on the electrical / Optical STM1 Port.

5. Perform 24-hour bit error test. 6. The configuration, delay analysis and results could

be stored in a file in most of the test equipments and can be exported to a PC/Laptop. It can also be printed directly by connecting a printer with the test equipment (Ant-5 or MTS-6000). A delay test was conducted for 18 hour.

3.5 Ethernet Performance Test

1. Create test environment as shown in figure-4 above.

2. Select Local Loopback mode in the Ethernet Test Equipment present on the far end.

3. Send ping packets and check the received packets. 4. The operation should be successful and returned

time should be within the normal range of 400 msec.

3.6 Ethernet Throughput Test

1. Create test environment as shown in figure-4 above.

2. Loopback the opposite equipment for throghpu test scenario.

3. Set the data network performance analyzer for the throughput test.

4. Use seven typical bytes for test: 64, 128, 256, 512, 768, 1024, and 1518.

5. Set allowed packet loss ratio to 0% and resolution to 0.1%. Test it for 60 seconds and repeat once again.

6. Carry out the test and record test result. 3.7 Ethernet Latency Test

1. Create test environment as shown in figure-4 above.

2. Loopback the opposite equipment for latency test scenario.

3. Set the data network performance analyzer for la-tency test settings.

4. Use seven typical bytes for test: 64, 128, 256, 512, 768, 1024, and 1518.

5. Set flow to 90% of the throughput. 6. Carry out the latency test and record test result. 7. Analyze Ethernet graph for latency limits within

1msec.

4 PROBLEM STATEMENT As the Authors mention in the research that Microwave radio link performance mainly depends on the high Sig-nal to Noise Ratio (SNR) values and low Bit Error Rates (BER) values. In the Microwave radio link trials, primarily

1.2 meter Directional Antenna was used, over a 47 Km hop distance. The Microwave system result was poor when STM-1 traffic was on air on the link, due to high Bit Error Rates (BER) values which result in low Signal to Noise Ratio (SNR) values, which causes high packet drop in the data transmission and result in high latency mar-gins above 1mec delays. Standard delay for Microwave radio link data transmission should be within 1 mesc lim-its, in order to run STM-1 traffic on the microwave link without packets drop and intruption. Hence by using 1.2 meter Directional Antenna, it was not feasible to run STM-1 traffic on the microwave link without packets drop and intruption which result in high latency limits ablove 1msec. Figure-5 shows the STM-1 latency test above 1msec delay, which causes high packet drop which result in high Bit Error Rates (BER) values and low Signal to Noise Ratio (SNR) values. Due to Bit Error Rates (BER) values and low Signal to Noise Ratio (SNR) values the desire through level is below 155 Mbps, which not feasi-ble to transmit STM-1 on Microwave radio link as shown in figure-6 [3, 4].

Figure-5 STM1 Latency Test

Figure-6 STM1 Throghput Test

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5 PROPOSED SOLUTION

In order to eleminte the problem of high packet drop which result in high Bit Error Rates (BER) values and low Signal to Noise Ratio (SNR) values, authors have pro-posed two paractical solution which are the fine tuning of Directional antennas and the use of 1.8 meter Directional Antenna, over a 47 Km hop distance. By increaseing the size of Directional Antenna the antenna gain increases which results in high Signal to Noise Ratio (SNR) values and low Bit Error Rates (BER) values which ultimately results in low packets drop during the data transmission over the Microwave radio link. Authors here have practically perform the fine tuning of 1.2 meter Directional antennas, which results in good re-sults in the form of high Signal to Noise Ratio (SNR) val-ues and low Bit Error Rates (BER) values which ulti-mately results in low packets drop during the data transmission over the Microwave radio link. This can be supported by results of Latency below 1 msec in figure-7 and through put rates upto 155 Mbps in figure-8 which is highly appropriate for running the STM-1 traffic over a Microwave radio link.

Figure-7 STM1 Latency Test

Figure-8 STM1 Throghput Test

6 CONCLUSION

Authors in this research have practically proved that

by fine tuning of 1.2 meter Directional Antenna, over a 47

Km hop distance we can improve the transmission of

STM-1 over the microwave link. Second the authors

have also proposed the increase of dish size which can

improve Signal to Noise Ratio (SNR) values which will result in low Bit Error Rates (BER) and no packet drop and

latency below than1 msec.

ACKNOWLEDGMENT

The authors wish to thank National Radio Telecom Cor-poration Haripur Hazara for their support in the trials of Long haulMicrowave radio link.

REFERENCES

[1] Online: www.airlinx.com.

[2] Online: www.otc.kz.

[3] Ramesh, S, and Herbert Tanzer, "The Design amd Performance

of a Lightwave data storage Network Using Computer Analysis

and Simulation, in Optical Switching/Networking and Com-

puting for Multimedia Systems, 2002.

[4] Mardeni, R. and Chimheno, R. L., "Wireless Regional Access

Networks: A Wise Choice for Internet Connectivity to Rural

Areas of Zimbabwe", Modern Applied Science, 2013. A. Qaddus received his BS Telecommuniactions from SZABIST Islama-

bad and had done MS Telecommunications & Networks from Bahria Uni-

versity Islamabad. Currently he is a PHD Scholar at Bahria University and is working as an A-EXEN in R&D Dept of National Radio Telecom Corpo-

ration Haripur, Hazara. His research interest includes, Wireless Communi-

cations, Computer Networks, RF Engineering and Data Communications.

M. Irfan received his BS Telecommuniactions form Paramount Islmabad

and done MS Electronic Engineering from MAJU Islamabad. Currently he

is working as an A-EXEN in R&D Dept of National Radio Telecom Corpo-ration Haripur, Hazara. His research interest includes, Wireless Communi-

cations, DSP and Data Communications.

A. Ali Raza received his BSEE from Urdu University Islamabad and had

done MS Telecommunications & Networks from Bahria University Islama-

bad. Currently he is a PHD Scholar at Bahria University His research inter-est includes, Wireless Communications, RF Engineering and Widercity.