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1 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
HSDPA Physical Layer Concepts
BangaloreApril 2007
2 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
Physical Layer Changes introduced for HSDPA
• Shorter Radio Frame(2ms instead of 10ms)
• New Downlink Data and Control Channel
• CDM combined with TDM
• 16 QAM Modulation Type (in addition to QPSK)
• New Uplink Control Channel
• Adaptive Modulation and Coding (AMC)
• Hybrid-ARQ (HARQ)
• New UE Capability Classes
3 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
HSDPA Frame Structure
• The HSDPA radio frame is 2 ms in length—equivalent to three of the currently defined W-CDMA slots
• It is actually a sub-frame in the W-CDMA architecture of 10ms
• There are five HSDPA sub-frames in a 10 ms W-CDMA frame, as shown in the Figure.
• The shorter frame size allows the UE to inform the network about failures every 2ms
• The network can respond more quickly to changing channel conditions and re-assign the capacity amongst users
4 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
New HSDPA Channels
5 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
New HSDPA Channels
DOWNLINK:• New Transport Channel:
– HS-DSCH: High Speed Downlink Shared Channel
• New Physical Channels:
– HS-PDSCH: High Speed Physical Downlink Shared Channel▪ Payload data
– HS-SCCH: High Speed Shared Control Channel▪ UE identity and HS-DSCH coding info
UPLINK:• New Physical Channels:
– HS-DPCCH: High Speed Dedicated Physical Control Channel▪ ACK, NAK and CQI (Channel Quality Indicator)
6 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
Downlink Physical Channel: HS-PDSCH
• Used to carry the HS-DSCH transport channel data
• Fixed Spreading Factor of 16 (SF = 16),
• A set of channelization codes (upto 15) are reserved for HS-DSCH transmission
• Turbo Coding (1/3) is used for channel coding
• Uses 16QAM Modulation scheme in addition to QPSK
HS-PDSCH
7 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
HS-PDSCH Configuration
8 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
HS-PDSCH Structure
• Data rate varies according Modulation Technique applied (QPSK/16QAM)
• Total no. of bits in a slot = M x 10 x 2K; – where k = 4, M = 2 or 4(QPSK or 16QAM)
• SF = 256/2k
• Max. Channel bit rate = 15 x 960 kbps = 14400 kbps, But this is the data rate after coding is applied
9 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
HS-PDSCH Channel coding
• Max. one transport block every TTI(2ms)
• CRC Length = 24 bits
• Bit Scrambling to remove continuous 0s or 1s
• Max. code block size = 5114 bits (Turbo Coding)
• Channel coding = 1/3 Rate Turbo Coding
• Hybrid-ARQ – 2 Stage Rate Matching
• Bits are mapped onto (up to 15) HS-PDSCH(s)
• Interleaving for each HS-PDSCH
• Different 16QAM constellations are defined
• Mapping to different HS-PDSCH(s)
10 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
Hybrid Automatic Repeat ReQuest (HARQ)
• Hybrid– Feed forward error correction, using turbo coding
– ARQ : Feedback error correction
• The Erroneous packets are not discarded but are combined with the retransmissions
11 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
Combining retransmissions
• To minimize the number of additional re-transmission requests
• HARQ can be operated in two different ways :– with identical retransmissions or
– with non-identical retransmissions
• Chase combining (CC) or Soft Combining – involves sending an identical version of an erroneously detected packet;
– received copies are combined by the decoder prior to decoding
• Incremental redundancy (IR) – involves sending a different set of bits incrementally to be combined with the original set,
– thus increasing the amount of redundant data and the likelihood of recovering from errors introduced on the air
12 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
Two Stage rate matching for IR
13 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
HS-PDSCH Channel coding - Example
14 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
Downlink Physical Channel: HS-SCCH
• Used to carry the control information needed for HS-DSCH decoding
• Fixed Spreading Factor of 128 (SF = 128)
• UE monitors one or more (upto 4) HS-SCCH channels to know when to receive data
• Uses QPSK modulation scheme
15 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
HS-SCCH Structure
• Slot #0 carries modulation information of HS-PDSCH:– Channelization Code Set (7 bits) (OVSF code assignment)
– Modulation Scheme: QPSK or 16QAM (1 bit)
• Slot #1, #2 carry channel-coding information of HS-DSCH:– Transport-block size (6 bits)
– Hybrid-ARQ process information (3 bits)
– Redundancy and constellation version (RV) (3 bits)
– New Data Indicator (NDI) (1 bit)
• The data of the 3 slots are covered with the 16 bit UE identity
16 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
HSDPA - Downlink Physical Channel Timing
• The NodeB transmits two slots of the HS-SCCH sub-frame before it begins transmitting the HS-PDSCH.
• The HS-SCCH and HS-PDSCH thus overlap during a slot (the third slot of the HS-SCCH).
• The 1st slot contains information of the channelization code set and modulation
• The UE must quickly decode the HS-SCCH, so that that UE does not miss the HS-PDSCH
17 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
Uplink Physical Channel: HS-DPCCH
• Used to carry the feedback information for HS-DSCH transmission– Acknowledgments (ACK) and Negative Acknowledgements (NAK)– Channel Quality Indicators to indicate quality of downlink transmission
• Fixed Spreading Factor of 256 (SF = 256)
• Uses BPSK Modulation scheme (One each for every HSDPA user)
18 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
• The 1st slot contains HARQ-ACK, 2nd and 3rd slots contains CQI• The HARQ-ACK information (1 bit) is coded to 10 bits,
– ACK coded as 1111111111– NAK coded as 0000000000
• The CQI information is coded using a (20,5) code• The feedback cycle of the CQI can be set as a network parameter in
predefined steps from 2 ms to infinity (disabled)• HARQ ACK/NAK response for every transmitted packet
HS-DPCCH Structure
19 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
HSDPA – Downlink & Uplink Physical Channel Timing
• HS-DPCCH is transmitted approximately 7.5 slots after its corresponding downlink HS-PDSCH sub-frame is received at the UE
• The timing of the ACK/NACK response from the UE on the HS-DPCCH is defined explicitly, so that the NodeB will know when to expect the response for each sub-frame it has transmitted.
20 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
Link Adaptation Techniques
• Two different Link Adaptation techniques are used
– Fast Re transmission using Hybrid Automation Repeat Request (H-ARQ)
– Adaptive Modulation and Coding (AMC)
21 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
Adaptive Modulation and Coding (AMC):
• Vary the downlink modulation and coding scheme depending on the channel conditions for each user
• 1/3 Turbo Coding is used, different effective code rates are obtained through various rate matching parameters
• Channel conditions reported by CQI in HS-DPCCH by the UE
• Modulation and coding can be adjusted Every 2 ms
22 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
Inter-TTI Interval
• Transmission Time Interval (TTI) is the time to transmit one data packet– For HSDPA its always 2 ms (=1 sub frame)
• Inter-TTI interval = number of TTIs (or subframes) between transmissions to the same UE
• All UEs must be capable of receiving transmissions at least every 3rd sub-frame (Minimum Inter-TTI interval = 3)
• More capable UE can handle Inter-TTI intervals of 2 or 1
Inter –TTI = 2
23 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
HARQ Processes
• If only 1 HARQ process is present, inter-TTI interval is at least 6 because arrival of ACK/NAK takes about 5 subframes
24 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
HARQ Processes
• Multiple parallel HARQ processes per user are possible:– Data rate to user is Increased
– Available system capacity is not wasted
25 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
HARQ Processes
• Throughput can be increased by reducing the inter-TTI interval (add more HARQ processes)
• UE w/ minimum inter-TTI = 3 supports 2 HARQ processes
• UE w/ minimum inter-TTI = 2 supports 3 HARQ processes
• UE w/ minimum inter-TTI = 1 supports the max. 6 processes
• Soft memory is partitioned across HARQ processes
• NodeB chooses no. of processes up to the max the UE can handle
26 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
UE Categories
27 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
Recap...
• Shorter Radio Frame(2ms instead of 10ms) allows to adapt quickly to channel conditions
• HS-PDSCH (Downlink Data)– Carries HS-DSCH data, SF = 16, 1/3 Turbo Coding, – Upto 15 Channelization Codes, TDM and CDM, 16QAM, – HARQ: 2Stage Rate Matching using Incremental Redundancy by varying Redundancy and Constellation Version
• HS-SCCH (Downlink Control)– Carries Control Information for HS-PDSCH, SF=128,– Channelization Code and Modulation Scheme, Transport Block Size, HARQ process no., RV and Constellation No.,
New Data Indicator, UE Identity
• HS-DPCCH (Uplink Control)– ACK/NAK, CQI
• Downlink and Uplink Physical Channel Timing– 2 slots between HS-SCCH and HS-PDSCH– Approximately 7.5 slots to receive a HS-DPCCH(ACK/NAK) at NodeB for a particular transmission
• Inter-TTI Interval – 3, 2 or 1
• HARQ Processes – 1 HARQ process: Inter-TTI = 6, so use multiple processes
28 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
Questions???
HSDPA Physical Layer Concepts
29 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
30 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
31 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
32 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
33 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
Backup Slide – Convolution Coding
Output 0G0 = 557 (octal)
InputD D D D D D D D
Output 1G1 = 663 (octal)
Output 2G2 = 711 (octal)
Output 0G0 = 561 (octal)
InputD D D D D D D D
Output 1G1 = 753 (octal)
(a) Rate 1/2 convolutional coder
(b) Rate 1/3 convolutional coder
34 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
Backup Slide – 1/3 Rate Turbo Coding
xk
xk
zk
Turbo codeinternal interleaver
x’k
z’k
D
DDD
DD
Input
OutputInput
Output
x’k
1st constituent encoder
2nd constituent encoder
35 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
Backup Slide – Interleaving
• Data of the form aaaabbbbccccddddeeeeffffgggg
will be transmittied as: abcdefgabcdefgabcdefgabcdefg
• To protect data transmission against burst errors
• Transmission without Interleaving:– Error-free message: aaaabbbbccccddddeeeeffffgggg
– Transmission with a burst error: aaaabbbbcccc____eeeeffffgggg
• Transmission with Interleaving:– Error-free transmission: aaaabbbbccccddddeeeeffffgggg
– Interleaved: abcdefgabcdefgabcdefgabcdefg
– Transmission with a burst error: abcdefgabcd____bcdefgabcdefg
– Deinterleaved with a burst error: aa_abbbbccccdddde_eef_ffg_gg
36 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
Backup Slide – HSDPA Cell Setup
37 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
Backup Slide – HSDPA Call Setup
38 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
Backup Slide – HS-SCCH 1st Slot UE id
• The HS-SCCH frame and the corresponding HS-PDSCH frame are overlapping by one timeslot
• UE has to first receive and decode the HS-SCCH frame before it knows whether the corresponding HS-PDSCH is addressed to it
• The UE identity can be resolved after reception of the first HS-SCCH timeslot
• The data in the 1st timeslot is masked using a bit string that is derived from the UE identity
• Only the correct UE identity can decode this timeslot
39 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
Backup Slide – HS-PDSCH Physical Layer HARQ function
• Two Stage Rate Matching and Incremental Redundancy
Systematicbits
Parity 1bits
Parity2bits
RM_P1_1
RM_P2_1
RM_P1_2
RM_P2_2
RM_S
First Rate Matching Second Rate MatchingVirtual IR Buffer
Nsys
Np1
Np2
Nt,sys
Nt,p1
Nt,p2
bitseparation
NTTIbit
collection
NdataC W
40 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
Backup Slide – CQI 20, 5 coding
• The code words of the (20,5) code are a linear combination of the 5 basis sequences denoted Mi,n defined in the table below
• The CQI values 0 .. 30 are converted from decimal to binary to map them to the channel quality information bits (1 0 0 0 0) to (1 1 1 1 1) respectively
• The channel quality information bits are a0 , a1 , a2 , a3 , a4 (where a0 is LSB and a4 is MSB). The output code word bits bi are given by:
where i = 0, …, 19.
i Mi,0 Mi,1 Mi,2 Mi,3 Mi,4 0 1 0 0 0 1 1 0 1 0 0 1 2 1 1 0 0 1 3 0 0 1 0 1 4 1 0 1 0 1 5 0 1 1 0 1 6 1 1 1 0 1 7 0 0 0 1 1 8 1 0 0 1 1 9 0 1 0 1 1
10 1 1 0 1 1 11 0 0 1 1 1 12 1 0 1 1 1 13 0 1 1 1 1 14 1 1 1 1 1 15 0 0 0 0 1 16 0 0 0 0 1 17 0 0 0 0 1 18 0 0 0 0 1 19 0 0 0 0 1
CQI value Transport Block Size
Number of HS-PDSCH
Modulation Reference power
adjustment NIR XRV
0 N/A Out of range
1 137 1 QPSK 0
2 173 1 QPSK 0
3 233 1 QPSK 0
4 317 1 QPSK 0
5 377 1 QPSK 0
6 461 1 QPSK 0
7 650 2 QPSK 0
8 792 2 QPSK 0
9 931 2 QPSK 0
10 1262 3 QPSK 0
11 1483 3 QPSK 0
12 1742 3 QPSK 0
13 2279 4 QPSK 0
14 2583 4 QPSK 0
15 3319 5 QPSK 0
16 3565 5 16-QAM 0
17 4189 5 16-QAM 0
18 4664 5 16-QAM 0
19 5287 5 16-QAM 0
20 5887 5 16-QAM 0
21 6554 5 16-QAM 0
22 7168 5 16-QAM 0
23 7168 5 16-QAM -1
24 7168 5 16-QAM -2
25 7168 5 16-QAM -3
26 7168 5 16-QAM -4
27 7168 5 16-QAM -5
28 7168 5 16-QAM -6
29 7168 5 16-QAM -7
30 7168 5 16-QAM -8
9600 0
2mod)(,
4
0Mab ni
nni
41 © Nokia Siemens Networks HSDPA Physical Layer Concepts / Bharat B / April 2007For internal use
Backup Slide – Other topics
• F- DPCH
• Associated DPCH channels
• Mapping of RV to Puncturing scheme
•