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General Packet Radio Service

VOCAL Technologies, Ltd. modem software libraries include a complete range of ETSI / ITU / IEEE compliant modulations, optimized for execution on ANSI C and leading DSP architectures (ADI, AMD-Alchemy, ARM, DSP Group, LSI Logic ZSP, MIPS and TI). This software is modular and can be executed as a single task under a variety of operating systems or it can execute standalone with its own kernel.

GPRS or General Packet Radio Service is a packet switched technology, based on GSM. The radio and network resources are only accessed when data actually needs to be transmitted between the mobile user and the network. This data is divided into packets and is then transferred via the radio and core network. Between alternating transmissions, no network resources need to be allocated.

GPRS offers up to 115 kbps, depending on the network availability, channel coding scheme and terminal capability. This increase in speed with respect to GSM is achieved by using more than one timeslot of the TDMA frame. Due to the packet switched characteristics the allocation of the available timeslots may vary from one instant to the next (e.g. it may have 8 timeslots at one time and 4 later on).

Timeslot building requires new functionality on the mobile side. GPRS needs a Serving support node (SGSN), a Gateway support node (GGSN) and a charging gateway function to support packet switched transactions. The packet switched traffic is separated from the circuit switched traffic at the BSC/PCU and diverted to the core network. To support point-to-multipoint features, a point–to-multipoint Service Center (PTM-SC) needs also to be added.

GPRS Terminology:

• Depending on the environmental radio conditions, one of the four coding schemes (CS1, CS2, CS3, CS4) can be selected. CS1 and CS2 offer good error detection and correction with low throughput; in the first step of only these two techniques may be used. CS3 and CS4 provide higher throughputs but have little or no error correction capabilities.

GPRS Features:

• Compliant with Layer 1 Radio.
• Compliant with Layer 1 Vocoder.
• Compliant with Layer 2 & 3 ETSI GSM phase 2+.
• Table 1 shows the different data rates that can be achieved with the different coding techniques:

Table 1 Data rates for GPRS

User Data Rate CS1 CS2 CS3 CS4
1 Timeslot 9.05 kbps 13.4 kbps 15.6 kbps 21.4 kbps
8 Timeslot 72.4 kbps 107.2 kbps 124.8 kbps 171.2 kbps

• Because it is packet switched traffic, new protocols and channel types are required. The mobile device is permanently attached to the network, providing a virtual connection without cost and data transfer (Attach). Attach procedure is executed whenever a enabled mobile station is switched on and needs to inform the network about its presence.
• The two peers of a attach procedure are the mobile station (MS) and the Serving Support Node (SGSN). Depending on the availability of the packet Common Control Channel (PCCCH), the Attach procedure may be executed on Circuit Common Control Channel (CCCCH).

• Figure 1 shows the GPRS system architecture, indicating new functionality required for phase2+ operation.

Figure 1. GPRS system architecture

GPRS Configurations:

Layer 1. Radio. This layer includes the following GSM phase2+ ETSI standards:

• GSM 05.02 Access & Multiple Multiplexing.
• GSM 05.03 Interleaving Code/Decoder Channel.
• GSM 05.04 Demodulator and Modulator.
• GSM 05.05 Receiver and Transmitter.
• GSM 05.10 Synchronization.

Layer 1.Vocoders. This layer includes the following GSM phase2+ ETSI standards:

• GSM 06.10 Full rate speech transcoding.
• GSM 06.20 Half rate speech transcoding.
• GSM 06.60 Enhanced Full rate speech transcoding.
• GSM 06.90 Adaptive multi-rate speech transcoding.
• GSM 06.93 Discontinuous transmission for Adaptive Multi-rate.

Layer 2 & 3 GSM phase 2+ ETSI standards:

• GSM 03.09 Hand-over.
• GSM 03.22 Link control.
• GSM 04.04 PROTOCOLS Layer 1.
• GSM 04.05 PROTOCOLS Layer 2.
• GSM 04.06 PROTOCOLS Layer 2.
• GSM 04.07 PROTOCOLS Layer 3.
• GSM 04.08 PROTOCOLS Layer 3.
• GSM 05.08 Power control.

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