As the basic 3G choice in China, TD-SCDMA has been widely accepted and adopted. The performance of China Communication Standard Association (CCSA) N-frequency TD-SCDMA DCH (Dedicated Channel) -based services has been well testified in both the trial and real networks. It is no question that DCH-based TD-SCDMA is able to provide both voice service and some packet services. Nowadays, for the ever-increasing demand on the multimedia services, the evolution of TD-SCDMA networks has become a hot issue. Single carrier TDSCDMA HSDPA (TD-HSDPA for short) was introduced in 3GPP in the R5 version as the downlink evolution of TD-SCDMA networks. Multi-carrier TD-HSDPA, introduced by CCSA, is the enhancement version of the 3GPP single carrier TD-HSDPA, which adopts the multi-carrier to improve the system performance. It offers backward-compatible upgrades to both former N-frequency TD-SCDMA networks and single carrier TD-HSDPA systems. In 2006, 3GPP made its effort to standardize the uplink evolution of TD-SCDMA networks. Released by 3GPP R6 version, TD-SCDMA HSUPA (TD-HSUPA for short) is believed to be able to enhance the system uplink capacity significantly. In order to offer the backward-compatible upgrade to both the N-frequency TD-SCDMA and multi-carrier TD-HSDPA, CCSA started the standardization work of multi-carrier TD-HSUPA in August, 2007. Armed with both the downlink and the uplink evolution, TD-SCDMA is believed to be able to provide various multimedia services. This article aims at introducing key concepts of the evolution of TDSCDMA networks, including system architecture, key techniques, protocols, and channels. The article begins with the introduction of the basic characters of TD-SCDMA. Then, the downlink evolution of TDSCDMA networks is presented. After that, we present the uplink evolution of TD-SCDMA networks. Key principles of TD-SCDMA Long-Term Evolution (LTE TDD) are discussed at the end of the article.
Basics Of Td-Scdma
Jointly developed by China Academy of Telecommunications Technology (CATT) and Siemens, TD-SCDMA is one of the IMT-2000 standards approved by the ITU. The main benefits of TD-SCDMA are that it can be implemented less expensively than the other comparable 3G systems since it is much more spectrum-efficient and is compatible with the current deployment of GSM network elements, allowing 3G asymmetric services without installation of completely new infrastructures.
Compared with WCDMA and CDMA 2000, TD-SCDMA adopts the TDD duplex mode and uses the same frequency band for both the uplink and the downlink. Meanwhile, the TDD mode has the adjustable switch point between the uplink and the downlink timeslots, which can adapt to the asymmetrical service in uplink and downlink and makes full use of the spectrum resource. Furthermore, the symmetrical channel feature of TDD systems makes it very flexible and convenient for TD-SCDMA to adopt the advanced techniques such as joint transmission, smart antenna, and so on, which can improve the system capability and spectrum efficiency. Key techniques that TD-SCDMA adopts include joint detection, smart antenna, dynamic channel allocation, and so forth. The interested reader is referred to Peng, Chen, and Wang (2007) and Peng and Wang (2007) for more information about key techniques of TD-SCDMA systems.
Key Terms in this Chapter
High-Speed Downlink Packet Access (HSDPA): The downlink evolution of TD-SCDMA networks; it aims at providing high downlink data rate to users
Hybrid Automatic Repeat reQuest (Hybrid ARQ): Another key technique in 3G evolution networks; a kind of ARQ method, in which retransmission occurs at the Media Access Control (MAC) layer, and information of different transmissions are combined at Physical (PHY) layer
Code Division Multiple Access (CDMA): A kind of multi-access method; users are distinguished in code domain. Other well-known multiple access methods are FDMA (frequency division multiple access), in which frequencies are used to distinguish different users, and TDMA (time division multiple access), in which time is used to distinguish different users.
High-Speed Uplink Packet Access (HSUPA): The uplink evolution of TD-SCDMA networks; it aims at providing high uplink data rate to users
Multimedia Service: An aggregation of different kinds of media, including text, image, video, audio, and so forth
Automatic Modulation and Coding (AMC): A key technique in 3G evolution networks; it adapts the modulation and coding format according to the channel quality
Time Division Duplex-Synchronous Code Division Multiple Access (TD-SCDMA): A 3G standard proposed by the China Academy of Telecommunications Technology (CATT) and Siemens jointly, and accepted by the ITU in 1999
Time Division Duplex (TDD): A kind of duplex mode; another well-known duplex is FDD (frequency division duplex) mode. Uplink (from user to network) and downlink (from network to user) in TDD mode are divided by time and FDD by frequency
Scheduling: Another key technique in 3G evolution networks; it decides which user should be severed, and at what data rate the user should be served
Quality of Service (QoS): A term which specifies the detail requirements on delay, delay jitter, packet loss, and data rate