Research on switching technology in WiMAX and TD-SCDMA Combination Network)

I. TD-SCDMA and WiMAX Technical Characteristics

In recent years, the most popular topic in the communication industry is the development of 3G and WiMAX technologies. In the 3G standard, the time-division Synchronous Code Division Multiple Access (TD-SCDMA) system, which is developed by China and has proprietary intellectual property rights, is particularly prominent. Compared with the other two 3G standard (WCDMA, CDMA 2000), the advantages of TD-SCDMA are: (1) the TD-SCDMA adopts the time-division digital Duplex (TDD) mode. TDD is a duplex mode for uplink and downlink transmission in the same frequency band. The uplink and downlink are differentiated and switched based on time. The time slot of the physical layer is divided into two parts: the uplink and downlink, and no paired frequency is required, upstream and downstream services share the same channel and can be unevenly distributed. This is especially suitable for Asymmetric grouped data exchange services (such as the Internet ). TDD features high spectrum utilization and low costs. (2) TD-SCDMA is the highest utilization of frequency resources. The TD-SCDMA system only uses 1.28 Mchip/s of the Code chip rate, using TDD duplex mode, only need to occupy a single 1.6 M bandwidth, can transmit 2 Mbit/s of data business. At the same time, the TD-SCDMA also has many shortcomings: (1) because of the multi-time slot discontinuous transmission mode, the base station transmission peak power to the average power ratio is high, resulting in a large base station power consumption, the base station has a small coverage radius, which also results in poor anti-fading and anti-Frequency Shift performance. When the mobile phone is in a high-speed mobile status, the communication capability is poor. (2) because the TD-SCDMA system only uses 1.28 Mchip/s bit rate, but the high bit rate can effectively use the frequency selective diversity and space receiving and transmitting diversity, it can effectively solve the problem of multi-path and fading. Therefore, it is difficult for users to fully meet the needs of high-speed multimedia services during high-speed data transmission.

WiMAX is a wireless MAN access technology. After a period of development, it has evolved from the first 802.16 standard to a series of standards such as 802.16a, 802.16d, and 802.16e. Taking WiMAX technology based on the IEEE 802.16d standard (fixed WiMAX technology) as an example, the coverage of a single base station can reach up to 50 kilometers, and the data bandwidth of each sector can reach up to 75 Mbit/s. In addition, wiMAX technology also features fast system construction, low cost, easy system expansion and upgrade, flexible frequency division and adjustment, and high QoS guarantee and Security at the Media Access Control (MAC) layer. The 802.16e technical standard is aimed at the lack of 802.16d standard mobility, so that users can still obtain high bandwidth when moving at the speed of vehicles.