17-12-2012, 02:54 PM
High Speed Packet Access - HSPA
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Abstract of HSPA
The High Speed Packet Access technology is the most widely used mobile broadband technology in communication world. It was already built in more than 3.8 billion connection with GSM family of technologies. The HSPA technology is referred to both High Speed Downlink Packet Access (3GPP Release 5) and to High Speed Uplink Packet Access (3GPP Release 6).
The Evolved HSPA technology or HSPA + is the evolution of HSPA that extends operator’s investments before the next generation’s technology 3GPP Long Term Evolution (LTE or 3GPP Release 8). The HSPA technology is implemented on third generation (3G) UMTS/WCDMA network and accepted as the leader in mobile data communication.
Using the HSDPA optimization on downlink is performed, whereas the HSUPA technology applying Enhanced Dedicated Channel (E-DCH) sets some improvements for the uplink performance optimization. The products that support HSUPA became available in 2007 and the combination of both HSDPA and HSUPA were called HSPA. Adopting these technologies the throughput, latency and spectral efficiency were improved.
Introducing HSPA resulted to the increase of overall throughput approximately to 85 % on the uplink and a rise more than 50 % in user throughput. The HSPA downlink available rates are 1 to 4 Mbps and for the uplink are 500 kbps to 2Mbps as of 1 quarter of 2009. The theoretical bit rates are 14Mbps at the downlink and 5.8 Mbps at the uplink in a 5MHz channel. Besides, the latency is notably reduced as well. In the improved network, the latency is less than 50ms, and after the introduction of 2ms Transmission Time Interval (TTI) latency is expected to be just 30ms.
The steps of the physical layer operation of the HSDPA:
• The scheduler in the Node B estimates the conditions of the channel, the pended data in the buffer, the expired time since the last session of the user and so on.
• After defining TTI for the terminal, the HS-DSCH parameters are assigned.
• In order to inform the terminal of the necessary parameters, the HS-SCCH two slots are transmitted by the Node-B before the corresponding HS-DSCH TTI.
• The given HS-SCCHs are monitored and after the decoding of the Part1 from an HSSCCHdetermined for that terminal, the rest of the HS-SCCH is decoded and terminalwill buffer the necessary codes from the HS-DSCH.
• As soon as the HS-SCCH parameters are decoded from Part 2, the terminal can define to which ARQ process the data belongs and the whether it is required the combine of the data and that already in the soft buffer.
• After the potentially combined data is decoded, the terminal sends ACK/NACK indicator in the uplink direction.
• If the transmission is performed in the same TTI the same HS-SCCH is used.