Before GPRS: HSCSD • HSCSD or High Speed Circuit Switched Data was the first upgrade to be standardized by ETSI to bring high speed data to GSM • The standardization process started as early as 1994 and therefore, HSCSD was the first high speed data extension to be ready for implementation in 1999 • Channel coding to increase the data rate from 9.6 kbps to 14.4 kbps • Up to 4 time slots combined per user. • HSCSD is able to reach throughput rates of up to 57.6 kbps
HSCSD Network Infrastructure • HSCSD is a circuit-switched technology • One of its major advantages is that the existing core network, mainly the MSC is able to handle HSCSD traffic. • As opposed to GPRS, HSCSD neither requires hardware upgrade within the network, nor does it introduces new channel coding methodologies. • HSCSD is a rather simple upgrade of the standard GSM, particularly in comparison with GPRS and EDGE.
GPRS • GPRS is a packet switched transmission • Provides the transmission of data in packet form • Switches data at packet level • Can always be online and users can be charged based on the amount of transmitted data rather than network time. • The radio and network resources are only accessed when data actually needs to be transmitted between the mobile user and the network • In between alternating transmissions, no network resources need to be allocated
GPRS • In circuit-switched transaction where resources are being accessed permanently, regardless of whether or not transmission is actually taking place
GPRS • Therefore, packet-switching saves resources, especially in the case of bursty transactions
GPRS • Packet overlay over existing GSM digital circuit switched network • Using packet-switching and is more suitable for bursty traffic • TCP/IP based (Allows data packets to be conveyed across network using packet switching • “Always on” / “Always connected” • After initial log-on, user is permanently connected to IP services • Bandwidth on demand • Network resources only used when data is ready to be transmitted • More efficient utilization of air time
Performance • GPRS offers bandwidths up to 160 kbit/s • GPRS applies timeslot bundling and new channel coding schemes have been defined, compared to GSM • With 8 timeslots and coding scheme 4, GPRS is able to provide a net throughput rate of 160 kbit/s • The channel coding schemes that provide for higher data transmission rates per slot sacrifices data protection for speed.
Performance • The new coding schemes CS-2, CS-3 and CS-4 make less provision for forward error correction and can only be applied when radio conditions are good to excellent
Network architecture • For GPRS, the existing network switching infrastructure cannot be reused. An entirely new core network architecture is required. • The base station subsystem or BSS can be used for both circuit-switched and GPRS packet-switched services. • BSS needs to be upgraded with the so-called Packet Control Unit or PCU • The new network elements within the GPRS core network are the serving GPRS node (SGSN) and the Gateway GPRS Support Node (GGSN)
EDGE • Formerly, EDGE was the abbreviation for Enhanced Data Rates for GSM Evolution • With EDGE being adopted by the North American market, EDGE is the acronym for Enhanced Data Rate for Global Evolution • EDGE introduces a new modulation scheme which is an 8-PSK in addition to GMSK in the case of GSM • GPRS and HSCSD works with the normal GSM modulation scheme which is GMSK. • GMSK has lots of advantages, the most important of which being that it does not contain any amplitude modulation. • Its low speed is one disadvantage. • In GMSK, only 1 bit can be transmitted per symbol, as opposed to 8-PSK where 3 bits are transmitted per symbol • This makes 8-PSK three times faster than GMSK
EDGE requires a major hardware upgrade • EDGE is mainly concerned with the modulation scheme on the Air-interface. • Adding 8-PSK as a new modulation scheme requires all base stations to receive hardware upgrades of their RF-parts to support the EDGE technology. • This is a major undertaking which is risky, and most importantly, costly to the operator.
EDGE (cont...) • Require h/w and s/w upgrade of both BS and MS • Used 8-PSK in addition to GMSK • Uses 9 air interface formats, known a multiple Modulation and Coding Schemes (MCS) autonomously and rapidly selectable for each time slot or user. Controlled by a feedback loop for maximum throughput with an acceptable outage performance • Using all 8 slots, can reach a max of 547 Kbps per user, practically 384Kbps per user per carrier.