Test Method for WiMax technology (1)

WiMax technology must reflect its own advantages in specific application scenarios in order to be recognized by the market. This requires application testing to measure system performance parameters. The test method of WiMax is divided into three parts: protocol analysis, radio frequency analysis, and transmission performance analysis. The Comprehensive Test results are obtained based on protocol analysis, radio frequency analysis, and transmission performance analysis.

WiMax Acceptance Test

An ideal test signal is required for WiMax amplifier and Module Testing. When performing performance tests on BS (base station), RS (trunk station), or SS (terminal) receivers, enter a test signal transmitted over a spatial channel.

The digital vector signal source SMU/SMJ/SMATE can generate WiMax signals that comply with specifications or user-defined specifications, including complete Wireless Frame settings, MAC (media access layer) settings, and channel coding.

Wireless Frame settings

OFDM Mode

Figure 1 shows the frame structure of the ofdm tdd mode.

Figure 1 frame mechanism in OFDM Mode

The downlink sub-frame consists of three parts: Preamble (Preamble), FCH (frame control header), and downstream data burst.

Preamble is located at the beginning of the sub-frame of the upper and lower lines. It is used for synchronization between the receiving and sending machines and channel estimation. The symbol structure can be divided into long preamble and short preamble: long preamble is used for downstream sub-frames and consists of two symbols. The first symbol appears every four sub-carriers, the second symbol appears every two subcarriers. Short preamble is used for uplink sub-frames. It is composed of one symbol and appears every two sub-carriers. If the downlink sub-frames transmit multiple data burst, the midamble between each burst is also short preamble.

FCH (Frame. control header) is located after Long Preamble and consists of a symbol. It contains the attributes of some system information such as the base station ID and DL data burst, which is used for receiver demodulation.

DL Burst contains mac pdu (protocol data unit) and broadcast information, such as DL-MAP, UL-MAP, DCD (downstream channel description), and UCD (Upstream Channel description ). A complete PDU consists of a 48-bit MAC Header, Payload (Data Segment), and cyclic redundancy check CRC.

In addition to the Preamble and ul pdu, the uplink sub-frame also contains the ranging (ranging) part. Ranging is a process in which the SS sends a request to BS to adjust the transmission power, latency, and frequency offset.

OFDMA Mode

Figure 2 shows the frame structure in OFDMA mode.

Figure 2 frame mechanism in OFDMA Mode

Because Access based on the logical subchannel (logical sub-channel) is introduced, the Wireless Frame Structure of OFDMA is more complicated. Figure 2 shows the frame structure plane composed of symbol number and subchannel number. Both the Preamble, FCH, broadcast information and data burst are distributed on this plane. The plane consists of a Zone and a segment, which are distinguished by symbol offset and subchannel offset.

Subchannels are divided into PUSC and FUSC, that is, subchannels are used in some cases and subchannels are used in all cases. subchannels are divided into six groups, and the number of subchannels is determined by the FFT Size, FFT Size 2048/1024/512/128 corresponds to 60/30/15/3 subchannels respectively.

RS signal source SMU currently supports Preamble, FCH, DL-map, UL-map, ranging, mac pdu (MAC Header

Ayload; CRC. For the OFDMA (WiBro) mode, up to 8 Zones and 3 segments can be configured.