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HSPA Evolution - CPC cont.

HSPA Evolution - CPC cont. [Under LTE > HSPA Evolution]
» Continuous connectivity for packet data - 25.903, Rel 7 «
» Physical channels and mapping onto transport channels - 25.211, Rel 7 «
» RRC - 25.331, Rel 7 «
» MAC - 25.321, Rel 7 «

DL DRX

Basic idea is UE to listen to downlink channels HS-SCCH, E-AGCH, and E-RGCH with configured DRX cycle. This DRX cycle is applicable once certain "inactivity threshold" is reached after last HS-DSCH actvity. Please refer Rel 6 channel mapping diagram in parallel to understand clearly.

As with UL DTX, HARQ operations are not to be impacted, so reception of E-HICH continues.

As noted in Rel 6 channel mapping article, F-DPCH is shared channel for power control when HSDPA and HSUPA are together. This channel need to be listened as per UL DTX cycle for power control.

Due to interdependency of UL and DL, it makes sense to have UL DTX and DL DRX implemented together.

Checkout related CPC-DRX/DTX article from wirelesstechbites blog for example diagrams on DTX/DRX.

HS-SCCH-less operation

Being HS-SCCH a shared (HSDPA) channel, at the face of it looks like we will not gain much by HS-SCCH-less operation. But that lot depend of HS-SCCH overhead over amount of data transmitted in HS-PDSCH. For VoIP services (where relatively smaller chunks of data are expected at moderately regular intervals), HS-SCCH overload is significant. In such cases, it makes sense to go for HS-SCCH-less operation (as per the VoIP simulation results detailed in 3GPP TS 25.903, Rel 7, sec 4.7.2.4).

As HS-SCCH-less opeation involve directly detecting HS-PDSCH, to make this work, upto 2 HS-PDSCH channelisation codes with 4 possible transport formats are employed (communicated using RRC setup signaling). Also, modulation of HS-PDSCH is fixed at QPSK. For UE identification (which used to be HS-SCCH), new 24-bit CRC method (2) is introduced which masks UE-Id.

When UE does not find signaling for itself in HS-SCCH in particular subframe(it signifies network is attempting HS-SCCH-less transmission), UE goes directly for detection on HS-PDSCH (sort of blind detection). If detection passes, UE answers with usual ACK; NACK for failure is not applicable as detection may fail as that transmission may not meant for the paricular UE. UE continue to listen to HS-SCCH.

Upon non-reception of ACK from UE (for attempted HS-SCCH-less transmission), network does re-transmission, but this time with HS-SCCH !

This process repeats. Refer related CPC article from wirelesstechbites blog for example diagrams.

HS-SCCH-less operation (which can work with Rel 5/6 HSDPA transmissions) can be combined with UL DTX or both UL DTX & DL DRX.

References: 3G Evolution: HSPA and LTE by Dahlman, Parkvall, Sköld, and Beming, UMTS by Sanchez and Thioune, and release 7 document at 3GPP.

Copyright © Samir Amberkar 2010-11§

HSPA Evolution - CPC « LTE Index » HSPA Evolution - MIMO