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    Edge Edge Presentation Transcript

    • EDGE Enhanced Data rates for GSM Evolution
    • EDGE Overview Enhanced data rates for GSM evolution (EDGE) is a major enhancement to the GSM data rates. Available data rates (GSM) can be increased from 9.6 kbps up to 64 kbps (HSCSD) and 160 kbps (GPRS). EDGE is specified in a way that will enhance the throughput per timeslot for both HSCSD and GPRS. The enhancement of HSCSD is called ECSD (enhanced circuit switched data), whereas the enhancement of GPRS is called EGPRS (enhanced general packet radio service). In ECSD, the maximum data rate will not increase from 64 kbps because of the restrictions in the A-interface, but the data rate per timeslot will triple. Similarly, in EGPRS, the data rate per timeslot will triple and the peak throughput, with all eight timeslots in the radio interface, will reach 473 kbps.
    • 8-PSK Modulation in GSM/EDGE Standard The ‘enhancement’ of tripling the data rates is the introduction of the 8-PSK (octagonal phase shift keying) modulation in addition to the existing Gaussian minimum shift keying. An 8-PSK signal is able to carry 3 bits per modulated symbol over the radio path, while a GMSK signal carries only 1 bit per symbol The increase in data throughput does not come for free, the price being paid in the decreased sensitivity of the 8-PSK signal. This affects, e.g. the radio network planning, and the highest data rates can only be provided with limited Coverage.
    • GSM Burst EDGE Burst
    • 8-PSK Modulation in GSM/EDGE Standard EDGE GSM The bit rate in the table is the gross bit rate. Part of the bits are used for error correction.
    • EDGE is specified in a way that will enhance the throughput per timeslot for both HSCSD and GPRS. The enhancement of HSCSD is called ECSD (enhanced circuit switched data), whereas the enhancement of GPRS is called EGPRS (enhanced general packet radio service).
    • EGPRS
    • EGPRS (enhanced general packet radio service) EGPRS is built on top of GPRS, which is the packetswitched data service of GSM. It includes nine different modulation and coding schemes (MCS-1–MCS-9) as well as related signalling and other procedures for link adaptation (switching between different MCSs). link adaptation also known as type 1 hybrid ARQ (Automatic Repeat-reQuest)
    • Link adaptation refers to a set of techniques where modulation, coding rate and/or other signal transmission parameters are changed on the fly to better adjust to the changing channel conditions. For example, EDGE uses a rate adaptation algorithm that adapts the modulation and coding scheme (MCS) according to the quality of the radio channel, and thus the bit rate and robustness of data transmission. Higher data rates can be offered with limited coverage and, therefore, the link adaptation mechanism becomes essential. Switching between 8-PSK- and GMSK-based channels is done with the standard intra-cell handover procedure
    • Table shows the EGPRS modulation and coding schemes (MCS) and their data throughputs. New GMSK coding schemes (MCS-1–MCS-4), different from GPRS GMSK coding schemes (CS-1–CS-4) are needed for the incremental redundancy. In incremental redundancy, also known as Type II Hybrid Automatic Repeat Request, retransmission of the data block is different to the initial transmission. Upon reception failure, additional redundancy is included which is combined with the earlier (re)transmission(s) and can thus be used to correct errors.
    • EGPRS (enhanced general packet radio service) in EGPRS, the data rate per timeslot will triple and the peak throughput, with all eight timeslots in the radio interface, will reach 473 kbps (59.2 x 3).
    • GPRS (general packet radio service) GPRS Coding Scheme Bit Rate (kbit/s/slot) Modulation Code Rate CS-1 8.0 GMSK 1/2 CS-2 12.0 GMSK ≈2/3 CS-3 14.4 GMSK ≈3/4 CS-4 20.0 GMSK 1
    • ECSD
    • HSCSD data rates HSCSD provides different levels of possible error correction which can be used according to the quality of the radio link. This means that in the best conditions 14.4 kbit/s can be put through a single time slot. The other innovation in HSCSD is the ability to use multiple time slots at the same time. Using the maximum of four time slots, this can provide an increase in maximum transfer rate of up to 57.6 kbit/s (i.e., 4 × 14.4 kbit/s).
    • ECSD (enhanced circuit switched data) ECSD uses current HSCSD as a basis. In ECSD, the maximum data rate will not increase from 64 kbps because of the restrictions in the A- interface, but the data rate per timeslot will triple. Data rates to be provided with ECSD, although limited to 64 kbps, are still sufficient for providing various transparent and non-transparent services.
    • Transparent bearer services use only the functions of the physical layer (layer 1 ISO/OSI reference model) to transmit data; data transmission consequently has a constant delay and throughput, that is if no errors occur. The only mechanism of any use to try and increase the quality of the transmission is forward error correction (FEC). This mechanism codes redundancy into the data-stream and Depending on the FEC, data rate of 2.4, 4.8, or 9.6 kbit/s are possible. Non-Transparent bearer services use protocols of the layers two and three to implement error correction and flow control. Nontransparent bearer services use the transparent bearer services, while adding a radio link protocol (RLP). This protocol uses mechanisms of high-level data link control (HDLC), and special selective-reject mechanisms to trigger retransmission of erroneous data. The achieved bit error rate is less than 10-7, but now throughput may vary, this depending on the transmission quality.
    • ECSD enables inter-working with audio modems at higher data rates than in current GSM networks, inter-working with ISDN at various data rates and various video-based services ranging from still image transfer to videoconferencing services.
    • EDGE vs GPRS
    • GPRS Airlink EDGE Airlink General Packet Radio Service (GPRS) Extends GPRS data with adaptive modulation Less spectral efficiency 2x spect. Eff. of GPRS for best effort data Same GMSK modulation as GSM 8-PSK/GMSK modulation 4 channel coding modes Adaptive coding techniques Packet-mode supports up to 115 kbps Supports peak rates over 384 kbps Flexible time slot allocation (1-8) Smart antennas & adaptive antennas Radio resources shared dynamically between speech and data services N/w based intelligent resource assignment Independent uplink and downlink resource allocation Downlink speeds at several Mbps based on wideband OFDM and/or multiple virtual channels
    • EDGE architecture
    • EDGE architecture
    • There are a number of key elements in the upgrade from GSM or GPRS to EDGE. The GSM EDGE technology requires a number of new elements to be added to the system: Use of 8PSK modulation: In order to achieve the higher data rates within GSM EDGE, the modulation format can be changed from GMSK to 8PSK. This provides a significant advantage in being able to convey 3 bits per symbol, thereby increasing the maximum data rate. This upgrade requires a change to the base station. Sometimes hardware upgrades may be required, although it is often simply a software change. Base station: Apart from the upgrade to incorporate the 8PSK modulation capability, other small changes are required to the base station. These are normally relatively small and can often be accomplished by software upgrades.
    • Upgrade to network architecture: GSM EDGE provides the capability for IP based data transfer. As a result, additional network elements are required. These are the same as those needed for GPRS and later for UMTS. In this way the introduction of EDGE technology is part of the overall migration path from GSM to UMTS. The two main additional nodes required for the network are the Gateway GPRS Service Node (GGSN) and the Serving GPRS Service Node (SGSN). The GGSN connects to packetswitched networks such as the Internet and other GPRS networks. The SGSN provides the packet-switched link to mobile stations. Mobile stations: It is necessary to have a GSM EDGE handset that is EDGE compatible. As it is not possible to upgrade handsets, this means that the user needs to buy a new GSM EDGE handset.