3GPP RAN Evolution

Second-generation GSM networks that were introduced in the early 1990s have experienced phenomenal growth over the last decade and have become the predominant wireless technology in the world today, with a market share of 70% or more. While the acceptance and numbers of subscribers in wireless cellular networks has been growing rapidly, the other phenomenon of the 1990s has been the exponential growth of the Internet and the number of Internet users. We have in essence a wireless network that primarily serves voice and messaging (SMS), and the Internet, which is a data-centric network that offers information, entertainment, e-commerce, and a slew of other services. With the natural evolution toward convergence of voice and data networks and the demand for Internet access and data services in wireless cellular networks, radio technologies defined for second-generation digital networks are evolving to accommodate packet data and services based on packet networks.
The initial GSM specifications provided only basic transmission capabilities for supporting data services. Data rates were in the 9.6-Kbps range. Release 96 specified high-speed circuit switched data services (HSCSD). The theoretical limit of HSCSD with 14.4-Kbps channel coding is 115.2 Kbps. However, practical limits allow data rates up to 64 Kbps.
After five years of intense standardization efforts, the result is an evolution path for GSM that is seen to be smooth, competitive, and cost-efficient. The first steps of this evolution were specified in Release 97 standards when GPRS was introduced. GPRS is able to deliver packet data services efficiently over existing GSM networks. The theoretical maximum throughput in GPRS networks is 160 Kbps per mobile station using all eight channels without error correction.
Voice capacity in wireless networks has always been an issue. In order to maximize the ROI (return on investment), operators have been asking for higher voice capacity over the existing spectrum. Adaptive multirate codec (AMR), which is included in Release 98, increased the spectral efficiency and quality of speech services significantly. The AMR codec contains a set of fixed-rate speech and channel codecs in addition to fast inband signaling and link adaptation. It operates in the full-rate and half-rate GSM channel modes.
Enhanced data rates for GDM evolution (EDGE) was introduced in Release 99. EDGE introduced more efficient modulation, coding, and retransmission schemes. The net effect of this was a significant boost to the performance of data services. EDGE as specified will enhance the throughput per time slot of both HSCSD and GPRS. Enhancement to HSCSD is called ECSD (enhanced circuit switched data), and enhancement to GPRS is called EGPRS (enhanced general packet radio service). ECSD in reality is not implemented since EGPRS is a superior mechanism for packet data access. The enhancement is equivalent to tripling the data rates for HSCSD and GPRS. This is accomplished by using 8-PSK modulation in addition to the existing GMSK. EGPRS is built on top of GPRS. One major change in EGPRS over GPRS is the link quality control, which in EGPRS also supports incremental redundancy. EGPRS also includes QoS capabilities that allow support for real-time services as well.