HSDPA(High speed downlink packet access).
In HSDPA some new fetures and new physical and transport channel are introduced.
CQI: channel quallity indicator
AMC: Adaptive modulation and coding.
H-ARQ: Hiybrid auo matic repeat request.
New MAC-HS entity.
Error correction using 1/3 turbo coding.
static TTI length of 3 timeslot= 2ms.
Below is new Physical channel intorduce:
1) HS-PDSCH(High Speed physical downlik shared channel).
this downlink channel used for both time and code multiplex.
chennalization code have fixed spreading factor=16
malticode transmissions are allowed that translates to UE being assigned multiplechannalization code in same TTI depending upon Mobile Capability.
same scrambling code are use to all applied channallization code that form single hs-dsch cctrch.
2) HS-SCCH(high speed shared control channel)
Fix rate of spreading factor:128 speed:60 kbps
carry downlink sgnaling related to HS-DSCH provide timing and coding information thus UE to listion HS-DSCH at correct time and coding information to allow succesfull decoding of UE data.
Main feture HSDPA
Fixed spreading factor 16 HS-DSCH
QPSK & 16 QAM modulation use.
static TTI 3 time slot=2 ms
error correction using 1/3 turbo coding.
New Transport channel :
1) HS-DSCH(High speed downlink shared channel):
This is downlink transport channel.
shared by several mobile phones.
it asociated with one downlink DPCH and one or several shared conrol channel HS-SCCH.
HS-DSCH is tranmitted over the entire cell or over only part ofcell using beam forming antennas.
for hs-dsch, the transport format indclluding the modulation scheme and code rate, can be selected on based on the downlik channel quality received on HS-DPCCH.
Transport format selection is done by MAC-hs located in Node-b and it based on channel quality feedback reportd by mobile.
Spreading code cannot change but the coding rate can change beween 1/4 and 3/4. higher coding rate can reduce the number error.
Up to 15 code can be allocated to Mobile
1code= 960 kbps so 15code to Mobile then 15*960= 14.4 mbps
so in HSDPA we get speed UP to 14.4Mbps in mobile.
CQI: Channel quality indicator
Information based on common pilot channel is used to estimat transport block size, modulation type and number of channalization codes.
HS-DSCH(High speed download shared channel)
HS-DSCH have some following feature
TTI-2ms for 3time slot. this is achived for short round trip delay for the operation beween terminal and Node-b for retransmission.
Adding higher order modulation scheem 16QAM increaasing data rate.
SF is fixed 16 and multicode transmission as well as code mux. of different user can tke place.
MUX. number of coe allocated is 15 depending on Mobile capability receive max 5, 10, or 15 codes.
this 15 code produce data rate 14.4 mbps.
SCCH(shared control channel):
This is downlink shared control channel.
Used to carry signalling to HS-DSCH transmission and coding information and indicate modulation qpsk or 16 QAM is used.
ARQ process number to indicate which ARQ is belongs to.
MAC-HS(Medium access control-high speed)
MAC-HS function is adaptive modulation and coding and fast shedulling are placed in NODE-B.
In release 99 transport format selection, schedulling are performed in RNC.
In HSDPA it is advantage to move this functionality from RNC to NODE-B.
MAC-HS handling schiduling, HARQ, Transport format selection.
There is one MAC-hs entity in each cel to support HS-DSCH. MAC-hs is resposnsible for data tranmiting on HS-DSCH.
it also resposible to managing the physica rsorce allocated to HSDPA.
MAC-hs recive configuration parameter from higher level.