Test the IAD performance in different WiMAX Wireless Environments

As a standard for wireless broadband MAN, WiMAX technology has great advantages over the previous 3.5GHzMMDS in terms of non-line-of-sight transmission and spectrum utilization efficiency. As one of the core of the Next Generation Network, the Softswitch Technology Based on the IP network is very mature in terms of comprehensive service access and QoS level assurance, and will replace the existing PSTN devices. This article describes the performance test results of softswitch IAD access in different WiMAX wireless environments, providing a flexible and convenient solution for the operator's "last mile" Integrated Service Access.

In order to improve the city image and improve the city environment in various regions, more and more communications and Overhead power lines will be placed in the ground. In addition, for new urban areas, development zones, and other places, in the initial planning, it will not allow the existence of overhead pole lines, which is a major challenge for the construction of access networks of basic telecom operators. In particular, the new fixed network operator does not have any access network resources. Even if the municipal department permits the construction of underground pipelines, the investment is not only very expensive, but irreversible. Therefore, carriers are looking for new access methods to replace wired access. New access methods must meet the convenient, fast, and cost-effective conditions to be accepted by operators. In the WIMAX environment, it is a good solution to provide users with comprehensive voice and data services through the integration of softswitch IAD.

Network topology and test environment

Network Topology 1

In this test, the external CPE is about 2 kilometers away from the WiMAX base station, which can meet different transmission conditions such as line of sight and non-line of sight. The IAD is configured with a listen 11 and an RJ45 interface, you can connect to common phones and data terminal devices separately. IAD can use DHCP, static IP, PPPoE, and other authentication access methods through static public IP address authentication ). Set the uplink/downlink bandwidth of CPE to 2 Mbit/s.

When an IAD user communicates with a PSTN user, the IAD user accesses the IP bearer network through the WIMAX wireless link, which is controlled by the media gateway controller Huawei SOFT3000) and sends the media stream to the integrated media gateway Huawei UMG8900 ), UMG8900 and PSTN Programmable switch Huawei CC08) have a direct circuit to complete communication.

When IAD users perform voice communication, they are controlled by the media gateway controller Huawei SOFT3000) and communicate through the IP bearer network.

Test results in different signal Environments

To achieve optimal access, WiMAX can automatically adjust the modulation mode of transmission signals according to different wireless environments. In the case of good signal conditions, it is generally line-of-sight (line-of-sight) transmission or partial occlusion. The QAM modulation method with high spectrum utilization is adopted. In the case of partial occlusion, the PSK modulation method is used; the BPSK modulation method is used for full occlusion and only propagation by reflection and refraction.

Line-of-sight transmission between 1 CPE and the base station, using QAM modulation

The test results show that the delay on the wireless side is 29 ms and no packet loss occurs during line-of-sight transmission between the CPE and the base station and the QAM modulation method. If no data is downloaded, the call is effective, which is no different from that of a common PSTN phone. The bandwidth occupied by a single voice is about 90 kHz. The real-time data transmission rate for downloading data on the website is basically 2 Mbit/s. Because IAD adopts the QOS priority assurance mechanism, the voice effect is basically the same as that for danchun calls.

In this environment, the signal strength of the Central Station and CPE is generally above-78dBm, And the CINR value is generally over 15.

2CPE and the base station are blocked but not very serious.

The test results show that when the CPE and the base station are blocked but not very serious, the PSK modulation method is adopted, because some signals must undergo refraction and reflection to reach the base station and the CPE, the latency of the wireless side is 49 ms, which is much higher than that of the QAM modulation, but there is no packet loss. At this time, the call effect is still very good, and the data can still be downloaded to 2 Mbit/s. Although the Call voice effect is somewhat decreased at the same time, it is acceptable.

In this environment, the signal strength of the central station is generally-87dBm or higher, and the strength of the CPE reception signal cannot be less than-82dBm, And the CINR value load-to-dry ratio is generally between 8 and 13.

3CPE blocks the base station heavily. When transmitted only through reflection, refraction, and other methods, the received signal is weak in intensity and interference is high. The BPSK modulation method is used.

The test results show that there is a severe occlusion between CPE and the base station. When the BPSK modulation method is used, the delay on the wireless side is 46 ms, which is much higher than that of the QAM modulation, the signal strength of the base station is-90dBm, and that of the CPE is-85dBm. This is the minimum value of the received signal strength when no packet loss occurs, if the CINR value is smaller than 6, packet loss will occur.) and the download speed cannot reach 2 Mbit/s, which is about 1.2 Mbit/s. At this time, the time for voice calls is still good, but the call effect is poor while downloading data.

Because the received signal strength of the base station and CPE is weak in the BPSK modulation mode, the signal declines greatly in the cloudy and rainy days when the weather changes ), the received signal strength and CINR value will decrease rapidly, which may cause problems such as packet loss and high latency, thus affecting the call quality. Therefore, when connected to voice users, it is recommended that the signal modulation method should be either in the QAM or the PSK mode, and the strength of the received signal of the CPE should be greater than-81dBm, the signal strength of the central station must be greater than-85dBm, And the CINR value must be greater than 8.

Summary

Due to the fixed testing location and environment, other problems may occur in actual applications, especially when the access environment is poor, the received signal strength and CINR value change greatly. However, we can see from the above test results that due to the adoption of OFDM technology, WiMAX has great advantages over other MMDS3.5GHz products in terms of NLOS transmission and spectrum utilization, in addition, IAD Based on Softswitch also has good adaptability in terms of latency and bandwidth, and has a strong QoS guarantee, therefore, WiMAX + Softswitch IAD is very suitable for Wired Access to difficult and costly development zones, small and medium-sized enterprise parks and other areas, it provides a good solution to solve the "Last Mile" access problem of operators.

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