GSM / GPRS / EDGE Evolution / VAMOS Fundamentals

GSM (Global System for Mobile Communications) networks have been deployed worldwide as second-generation mobile communications systems. GSM originally was developed to transmit voice, but it is also able to transmit data with a max. load of 9.6 kbit/s in the downlink and uplink. With the technical interim solution HSCSD, the max. data rate was increased to 43.2 kbit/s in the downlink and 14.4 kbit/s in the uplink.

Packet data capabilities were added in the Release '97 version of the GSM standard by means of GPRS (General Packet Radio Services). GPRS is a data service that is available to users of GSM and IS-136 handsets. GPRS can be used for all data services such as Internet browsing, WAP access, SMS and MMS. Unlike GSM, GPRS is packet-switched; in terms of multiple users, it shares the same transmission channel only when data must be sent. The achievable data rates in GPRS depend on the supported multislot class. The max. data rate per time slot is 21.4 kbit/s with a max. possible number of 8 slots in either the downlink or uplink direction. A multislot class 10 mobile device, for example, supports max. 4 Rx slots in the downlink and max. 2 Tx slots in the uplink, but the sum of both Rx and Tx slots is max. 5.

To increase the data transmission rate and to improve network capacity, EDGE (Enhanced Data for GSM Evolution) was introduced in Release '98. With EDGE, a new modulation scheme is applied: 8PSK (phase shift keying), i.e. three bits per RF modulated symbol as opposed to the original one bit per symbol in GPRS. This technology change triples the effective data rate for EDGE, resulting in a peak date rate of 59.2 kbit/s per time slot. Similar to GPRS, the maximum achievable data rate depends on the supported multislot class of the mobile device. The average downlink data rate in commercially operated networks is in the range of 300 kbit/s. EGPRS is a superset expression comprising EDGE and GPRS.

EDGE Evolution contains a set of features specified in 3GPP Release 7. The primary motivation for enhancing EDGE is to ensure the future competitiveness of the dominant second-generation technology and specifically to provide service continuity across the various radio technologies (GERAN, UTRAN, LTE) supported by core network evolution, e.g. IMS. The improvements include downlink dual carrier (DL DC) operation, higher order modulation (EGPRS2 with 16QAM and 32QAM) in combination with an optional higher symbol rate (Level B) and turbo coding in downlink, latency improvements, and the use of Rx diversity at the mobile station. Combining DL DC and EGPRS2 Level B, peak data rates reach up to 1.9 Mbit/s in the downlink, whereas realistically data rates of 1 Mbit/s will be achieved.

VAMOS is one of the most important features added in 3GPP Release 9 as it has the potential to double the voice capacity in the GSM network. The new AQPSK modulation scheme in DL enables allocation of different power levels on the I and Q phase. In combination with new orthogonal training sequences, two voice users can share the same physical resource.

In 1989, the GSM standard was defined by the Groupe Speciale Mobile and became an internationally accepted digital cellular telephony standard. GSM was later transferred to the ETSI technical committee, which continued to define the GSM standards. Today, GSM and EDGE are being specified in 3GPP (3rd Generation Partnership Project) and coordinated in TSG GERAN.

GSM / GPRS / EDGE Evo / VAMOS at Rohde & Schwarz

Rohde & Schwarz provides a complete product portfolio for GSM/GPRS/EDGE: digital standards on general-purpose equipment such as vector signal generators and signal and spectrum analyzers; dedicated communications testers and complete conformance test systems. The latest enhancements including EDGE Evolution functionality and the VAMOS feature are supported, while future implementations will reflect the latest 3GPP enhancements. Rohde & Schwarz has been offering products since the early launch of GSM on the market and therefore understands all aspects of implementing this truly global technology.

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