3G Cellular Systems

Around the world, mobile operators are upgrading their networks to 3G technology to deliver broadband applications to their subscribers. Mobile operators using GSM (global system for mobile communications) are deploying UMTS (universal mobile telephone system) and HSDPA (high speed downlink packet access) technologies as part of their 3G evolution. Traditional CDMA operators are deploying 1x EV-DO (1x evolution data optimized) as their 3G solution for broadband data. In China and parts of Asia, several operators look to TD-SCDMA (time division-synchronous CDMA) as their 3G solution. All these 3G solutions provide data throughput capabilities on the order of a few hundred kilobits per second to a few megabits per second.

HSDPA is a downlink-only air interface defined in the Third-generation Partnership Project (3GPP) UMTS Release 5 specifications. HSDPA is capable of providing a peak user data rate (layer 2 throughput) of 14.4Mbps, using a 5MHz channel. Realizing this data rate, however, requires the use of all 15 codes, which is unlikely to be implemented in mobile terminals. Using 5 and 10 codes, HSDPA supports peak data rates of 3.6Mbps and 7.2Mbps, respectively. Typical average rates that users obtain are in the range of 250kbps to 750kbps. Enhancements, such as spatial processing, diversity reception in mobiles, and multiuser detection, can provide significantly higher performance over basic HSDPA systems. It should be noted that HSDPA is a downlink-only interface; hence until an uplink complement of this is implemented, the peak data rates achievable on the uplink will be less than 384kbps, in most cases averaging 40kbps to 100kbps. An uplink version, HSUPA (high-speed uplink packet access), supports peak data rates up to 5.8Mbps and is standardized as part of the 3GPP Release 6 specifications; deployments are expected in 2007. HSDPA and HSUPA together are referred to as HSPA (high-speed packet access).

1x EV-DO is a high-speed data standard defined as an evolution to second-generation IS-95 CDMA systems by the 3GPP2 standards organization. The standard supports a peak downlink data rate of 2.4Mbps in a 1.25MHz channel. Typical user-experienced data rates are in the order of 100kbps to 300kbps. Revision A of 1x EV-DO supports a peak rate of 3.1Mbps to a mobile user; Revision B will support 4.9Mbps. These versions can also support uplink data rates of up to 1.8Mbps. Revision B also has options to operate using higher channel bandwidths (up to 20MHz), offering potentially up to 73Mbps in the downlink and up to 27Mbps in the uplink. In addition to providing high-speed data services, 3G systems are evolving to support multimedia services. For example, 1x EV-DO Rev A enables voice and video telephony over IP. To make these service possible, 1xEV-DO Rev A reduces air-link latency to almost 30ms, introduces intrauser QoS, and fast intersector handoffs.