 almost every available technology. TD-SCDMA flexibly allocates air-interface resources using four different technolo- gies for dividing the available capacity of the air interface: time division, code division, frequency division, and space division.¹ In addition, it is optimized for practical data applications. In addition to supporting variable bandwidth in each direction, it has spe- cial features to support a variable bandwidth ratio, a key support factor for Internet browsing, graphical downloads, and other data functions. In this section we will explain how multiple technologies were brought together to optimize the potential for the air interface in the standard that the People's Re- public of China has chosen for its cellular deployment to the world's largest subscriber market. 10.4.1 TD-SCDMA services TD-SCDMA offers the entire suite of 3G wireless voice and data services. Symmetric voice and data service are supported, and they can migrate smoothly to asymmetric data service where most of the flow is in one direction. Reverse data rates go up to 384 kbps, whereas forward data rates can go as high as 2 Mbps under the most favorable radio conditions. All these data services are available in circuit or packet mode engi- neered for efficient IP data service. 10.4.2 TD-SCDMA voice channel The speech data rate for TD-SCDMA is 8 kbps. A single carrier can handle as many as 48 simultaneous voice calls with a spectrum efficiency three times greater than GSM. The technology is designed for smooth migration from GSM while increasing spectral efficiency by a factor of 3. Simulations show the 1.6-MHz TD-SCDMA carrier handling 28 calls per cell at 60 km/h, 24 calls per cell at 120 km/h in the city, and 22 calls per cell at 120 km/h in a rural setting. 10.4.3 TD-SCDMA radio bandwidth TD-SCDMA uses a TDD carrier of 1.6 MHz. There is no FDD mode because the TD- SCDMA research is clearly oriented toward serving a voice and data market that can be balanced in its forward and reverse usage and can be highly asymmetric wit