1. UMTS Evolution High Speed Packet Access (HSPA)
There were number of pushing forces to improve the packet data capabilities of WCDMA even further, e.g.
Growing interest towards rich calls, mobile-TV and music streaming in the wireless domain
Competitive technologies such as WIMAX
High Speed Packet Access (HSPA) evolution introduced first downlink counterpart of the evolution called High Speed Downlink Packet Access (HSDPA) in Release 5
Uplink evolution followed later in Release 6 by the name of High Speed Uplink Packet Access (HSUPA)
HSPA was originally designed for non-real time traffic with high transmission rate requirements

2. HSPA Features HSPA features/properties include e.g.
Higher order modulation and coding
Higher throughput and peak data rates
In theory up to 5,8 Mbps in the uplink and 14 Mbps in the downlink without Multiple Inputs and Multiple Outputs (MIMO)
Multiple Inputs and Multiple Outputs (MIMO)
Roughly speaking equals to additional transmitter and receiver antennas
Fast scheduling in the Node B
Possibility to take advantage of channel conditions with lower latency
Link adaptation in downlink
Possibility to adjust the used modulation and coding scheme according to be appropriate for current radio channel conditions
Improved retransmission capabilities
Newly introduced layer one retransmissions called as Hybrid Automatic Repeat Request (HARQ) => reduced delay
Radio Link Control (RLC) level retransmissions still possible
Shorter frame sizes and thus Transmission Time Intervals (TTI)
With HSDPA 2ms and with HSUPA 10ms and 2ms
© 2008 Magister Solutions Ltd

3. WCDMA Background and Evolution
3GPP Rel 5 (HSDPA)
03/02
3GPP Rel 6
(HSUPA)
2H/04
3GPP Rel 7
HSPA+
06/07
3GPP Rel -99
12/99
3GPP Rel 4
03/01
Further Releases, (LTE)
2000
2001
2002
2003
2004
2005
2006
2007
Japan
Europe
(pre-commercial)
Europe
(commercial)
HSDPA (commercial)
HSUPA (commercial)

4. High Speed Downlink Packet Access (HSDPA)
Designed for data service applications.
Aimed to provide, for the downlink, significant reduced delay and peak rates up to 8-10 Mbps.
Fully Release 99 backward compatible.
Can co-exist on the same RF carrier with Rel’99 UMTS traffic.

5. Introduction to HSDPA (1/2)
In Release 99 there basically exists three different methods for downlink packet data operation
DCH
Forward Access Channel (FACH) and
Downlink Shared Channel (DSCH)
After the introduction of HSDPA in Release 5 some changes to downlink packet data operations occurred
New High Speed DSCH (HS-DSCH) channel was introduced (High Speed Downlink Packet Access “HSDPA” )
DSCH was removed due to lack of interest for implementing it in practical networks

6. Introduction to HSDPA (2/2)
HSDPA Improvements for packet data performance both in terms of capacity and practical bit rates are based on
The use of link adaptation,
Higher order modulation,
Fast scheduling,
Shorter frame size (or transmission time interval), and
Physical layer retransmission
HSDPA does not support DCH features like fast power control or soft handover
© 2008 Magister Solutions Ltd

7. HSDPA channels (1/3)
The Release 99 based DCH is the key part of the system – despite the introduction of HSDPA
Release 5 HSDPA is always operated with the DCH
DCH with HSDPA
If the service is only for packet data, then at least the signaling radio bearer (SRB) is carried on the DCH
In case the service is circuit-switched then the service always runs on the DCH
With Release 6, signaling can also be carried without the DCH
In Release 5, uplink user data always go on the DCH (when HSDPA is active)

8. HSDPA channels (2/3)
in Release 6 an alternative is provided by the Enhanced DCH (E-DCH) with the introduction of high-speed uplink packet access (HSUPA)
User data is sent on High Speed Downlink Shared Channel (HS-DSCH)
Both time and code shared between users.
Within each 2msec Transmission Time Interval (TTI), a constant spreading factor of 16 is used with a maximum of 15 parallel codes.
2 to 4 users can share the code resources with the same TTI.
Control information is sent on High Speed Shared Control Channel (HS-SCCH)
HS-SCCH carries information to decode HS-DSCH (Modulation, block size,..etc.), SF=128.
HS-SCCH is sent two slot before HS-DSCH to inform the scheduled UE of the transport format of the incoming transmission on HS-DSCH

9. HSDPA channels (3/3) New uplink physical channel:
HS-DPCCH (High speed-Dedicated Physical Control Channel).
Indicates the channel quality indicator (CQI) used for fast link adaptation.
Carries the acknowledgment signal for retransmission process.
Spreading Factor =256.

10. Link Adaptation (1/3)
UE informs the Node B regularly of its channel quality by CQI messages (Channel Quality Indicator)

11. Link adaptation adjusts the mode within few ms based on CQI
Adaptive modulation and higher order modulation (16/64QAM) with HSDPA
Link adaptation adjusts the mode within few ms based on CQI

12. Link Adaptation (3/3)
More complex modulation schemes require more energy per bit to be transmitted than simply going for transmission with multiple parallel code channels, thus HSUPA benefits more from using multiple codes as PC keeps the signal levels quite good anyway

13. Fast Retransmissions (1/3)
Rel ‘99
HSPA
RNC
Retransmisson
Packet
Packet
NodeB
RLC ACK/NACK
Retransmisson
Layer 1 ACK/NACK UE
Radio Link Control (RLC) layer ACK/NACKs also possible with HSPA

14. Fast Retransmissions (2/3)UE
NodeB
RNC
User data
(Re)transmission
RLC
RLC (N)ACK
MAC-d
MAC-hs
(Re)transmission
Layer1
HARQ (N)ACK

15. Fast Retransmissions (3/3)
Layer 1 signaling indicates the need of retransmission which leads to much faster round trip time that with Rel ‘99
Retransmission procedure with layer 1 retransmissions (HARQ) is done so that decoder does not get rid of the received symbols if the transmission fails but combines them with new transmissions
Retransmissions can operate in two ways:
Identical retransmissions (soft/chase combining)
Non-identical retransmissions (incremental redundancy)

16. Downlink scheduling (1/5)
NodeB has certain amount of users connected to it and it needs to schedule the different users for transmission in different fractions of time (Transmission Time Intervals)
Certain fairness for scheduling time for each user should be maintained
Resources should be utilized in optimal manor
There exists different ways that users can be scheduled in downlink, e.g.
Round Robin
Proportional Fair

17. Downlink scheduling (2/5)
Round Robin (RR)
Simplest scheduling algorithms
Assigns users in order i.e. handling all users without priority
Positive sides
Easy to implement
Each user gets served equally
Negative sides
No channel conditions are taken into account and thus resources might be wasted

18. Downlink scheduling (3/5)
Proportional Fair (PF)
Compromise-based scheduling algorithm
Based upon maintaining a balance between two competing interests
Maximize network throughput i.e. users are served in good channel conditions
Allowing all users at least a minimal level of service

19. Downlink scheduling (4/5)
PF assigning each users a scheduling priority that is inversely proportional to its anticipated resource consumption
High resource consumption => low priority

20. Downlink scheduling (5/5)
In general priority metric for certain user can be defined as follows
where instantaneous data rate, d, is obtained by consulting the link adaptation algorithm and average throughput, r, of the user is defined and/or updated as follows
where is so called forgetting factor. Hence, equals the equivalent averaging period in a number of TTIs for the exponential smoothing filter 20

21. Mobility with HSDPA (1/4)
Handovers are roughly tradeoff between two issues
When channel conditions are getting worse, handover to better cell should be made so that packets won’t get lost due to poor channel conditions
However, each time when the handover is made, transmission buffers in the Node B are flushed resulting to additional delays from RLC level retransmission or disruption of service
When regarding HSDPA, the user can be connected only to one serving HSDPA Node B at the time
Leading to hard handover when the handover between HSDPA Node Bs is required in contrary to DCH soft handover

22. Mobility with HSDPA (2/4)
Even though there is only one serving HS-DSCH cell, the associated DCH itself can be in soft(er) handover and maintain the active set as in Rel’99
Node B,
Serving HSDPA
DCH
DCH
Node B,
Part of DCH active set
HS-SCCH UE
DCH/HSDPA
DCH

23. Mobility with HSDPA (3/4)
HSDPA handover procedure includes following steps
Serving HS-DSCH cell change procedure is initiated when a link in (DCH) active set becomes higher in strength and stays stronger for certain period of time, referred as time-to-trigger
If the condition mentioned above is met then the measurement report is sent from the UE to the Node B, which forwards it to the RNC
If e.g. the admission control requirements are met the RNC can then give the consent for the UE to make the handover by sending so called Signaling Radio Bearer (SRB) (re)configuration message

24. Mobility with HSDPA (4/4)
In the case of intra Node B handover, the HARQ processes (transmissions) and Node B buffers can be maintained and thus there is only minimal interruption in data flow
However, with inter Node B handover i.e. between Node Bs, the Node B packet buffers are flushed including all unfinished HARQ processes which are belonging to the UE that is handed off

25. High Speed Uplink Packet Access (HSUPA)

26. Introduction to HSUPA (1/2)
Roughly three years later when HSDPA was introduced uplink counterpart of the high speed packet access evolution was introduced in Release 6
In 3GPP original name was not HSUPA but Enhanced Dedicated Channel (E-DCH)
The obvious choices for uplink evolution was to investigate the techniques used for HSDPA and, if possible, adopt them for the uplink as well
Improvements in HSUPA when compared to Rel’99
Layer 1 Hybrid ARQ (HARQ) i.e. fast retransmissions
Node B based scheduling

27. Introduction to HSUPA (2/2)
Easier multicode transmissions
Shorter frame size, 10ms mandatory for all HSUPA capable devices and 2 ms as optional feature
HSUPA is not a standalone feature, but requires many of the basic features of the WCDMA Rel’99
Cell selection and synchronization,
random access,
basic power control loop functions,
basic mobility procedures (soft handover), etc.

28. HSUPA channels (1/4)
New uplink transport channel - Enhanced Dedicated Channel (E-DCH)
Supports key HSUPA features such as HARQ, fast scheduling etc.
Unlike HS-DSCH (HSDPA) E-DCH is not a shared channel, but a dedicated channel (*)
Similarly to DCH, E-DCH is also mapped to physical control and data channels
The user data is carried on the enhanced dedicated physical data channel (E-DPDCH) while new control information is on the E-DPCCH
(*)Dedicated channel means that each UE has its own data path to the Node B that is
continuous and independent from the DCHs and E-DCHs of other UEs

29. HSUPA channels (2/4)
From the Release 99 DCH, the dedicated physical control channel (DPCCH) is unchanged and the need for the DPDCH depends on possible uplink services mapped to the DCH
DPCCH is used e.g. for fast power control
New channels for scheduling control
E-DCH absolute grant channel (E-AGCH) - absolute scheduling value
E-DCH relative grant channel (E-RGCH) - relative step up/down scheduling commands

30. HSUPA channels (3/4)
New channel for retransmission control, carries information in the downlink direction on whether a particular base station has received the uplink packet correctly or not
E-DCH HARQ indicator channel (E-HICH)

31. HSUPA channels (4/4) DPCCH NodeB E-DPCCH E-DPDCH E-RGCH UE E-AGCH
E-HICH

32. Uplink scheduling (1/5)
With HSDPA all the cell power can be directed to a single user for a short period of time
Very high peak data rates achievable for certain UE and all the others can be left with a zero data rate
However, in the next time instant another UE can be served and so on
With HSUPA, HSDPA type of scheduling is not possible
HSUPA is a many-to-one scheduling
The uplink transmission power resources are divided to separate devices (UEs) which can be used only for their purposes and not shared as with HSDPA

33. Uplink scheduling (2/5)
The shared resource of the uplink is the uplink noise rise(*), or the total received power seen in the Node B receiver
Typically, one UE is unable to consume that resource alone completely and it is very beneficial for the scheduler to know at each time instant how much of that resource each UE will consume and to try to maintain the interference level experienced close to the maximum
Thus, HSUPA scheduling could be referred as very fast DCH scheduling
(*)ratio between the total power received from all of the UEs at the base station and the thermal noise

34. Uplink scheduling (3/5)
Two different scheduling schemes are defined for HSUPA traffic
Scheduled transmissions controlled by Node B which might not guarantee high enough minimum bit rate. In addition each request requires time consuming signaling
Non-scheduled transmissions (NST) controlled by radio network controller (RNC) which defines a minimum data rate at which the UE can transmit without any previous request. This reduces signaling overhead and consequently processing delays

35. Uplink scheduling (4/5) Scheduled transmissions
The scheduler measures the noise level and decides whether
Additional traffic can be allocated
Should some users have smaller data rates
The scheduler also monitors the uplink feedback
Transmitted on E-DPCCH in every TTI
Referred as happy bits
Tells which users could transmit at a higher data rate both from the buffer status and the transmission power availability point of view

36. Uplink scheduling (5/5)
Depending on possible user priorities given from the RNC, the scheduler chooses a particular user or users for data rate adjustment
The respective relative or absolute rate commands are then send on the E-RGCH or E-AGCH
UE in soft handover receives only relative hold/down commands from other than serving HSUPA Node B

37. Multicodes with HSUPA (1/2)
Even though Rel’99 DCH supports in theory multicode transmissions in practice only E-DCH can support multicode transmissions and thus higher bitrates
In theory DCH can use 6xSF4 leading to 5.4 Mbps
E-DCH can in practice support 2xSF2 + 2xSF4 leading to 5.4 Mbps
The reason why DCH does not support multicodes is that the DCH is controlled by RNC and thus DCH is rather slowly controllable

38. Multicodes with HSUPA (2/2)
If the UE could send with fully utilizing multicodes in some time instant this might not be the case later and UE might end up in power outage and thus wouldn’t be able to use its allocation
With RNC control reallocation of resources is slow => resources wasted
Also, HSUPA with HARQ increases the possibility to operate with higher BER target which leads to lower power requirement for corresponding data rate

39. Mobility with HSUPA (1/2)
HSUPA supports the soft(er) handover procedure similar to WCDMA Rel’99
The HARQ operation in HSUPA soft handover situation is done in following manor
If any Node B part of the active set sends an ACK, then the information given to the Medium Access Control (MAC) layer is that an ACK has been received and the MAC layer will consider the transmission successful

40. Mobility with HSUPA (2/2)
Packet reordering
RNC
Correctly received packet
NodeB
Layer 1 ACK/NACK
Data
NodeB UE
Layer 1 ACK/NACK

41. Continuous Packet Connectivity (CPC)

42. Continuous Packet Connectivity (1/5)
Continuous Packet Connectivity (CPC) was released in Release 7
Designed to improve the performance of delay critical small bit rate services like VoIP
Eliminates the need for continuous transmission and reception when data is not exchanged. Can be categorized into three feature
UL discontinuous transmission
DL discontinuous transmission
HS-SCCH less for HSDPA VoIP

43. Continuous Packet Connectivity (2/5)
Benefits
Connected inactive HSPA users need less resources and create less interference => more users can be connected
UE power savings => increased talk time (VoIP)
UTRAN resources are saved

44. Continuous Packet Connectivity (3/5)
12.2 kbps DCH
R99 DCH with 20-ms TTI (Rel’99, CS voice)
32 kbps E-DCH
E-DCH with 10-ms TTI
(Rel’6, phase 1, VoIP)
160 kbps E-DCH
Power offset
E-DCH with 2-ms TTI
(Rel-6, phase 2, VoIP)
160 kbps E-DCH
E-DCH with 2 ms TTI and UL DPCCH gating
(Rel-7, VoIP) PO
= DPDCH (DCH) / E-DPDCH (E-DCH)
= DPCCH

45. Continuous Packet Connectivity (4/5)
DL discontinuous transmission or Discontinuous Reception (DRx) cycles allow an idle UE to power off the radio receiver for a predefined period
Period after the UE wakes up again is called as DRx cycle
When UE wakes up it listens predefined time for incoming transmissions and if it successfully decodes a new transmission during that time it starts timer for staying active certain period of time
No measurements done or data received

46. Continuous Packet Connectivity (5/5)
HS-SCCH-less HSDPA operation in downlink
Initial transmission of small (VoIP) packets can be sent without High Speed Secondary Control Channel (HS-SCCH)
Eliminates the control channel overhead from small packets sent over HSDPA
Retransmissions are sent with HS-SCCH pointing to the initial transmission

47. Internet HSPA (I-HSPA) or HSPA+

48. I-HSPA (1/2)
Internet-HSPA (I-HSPA) aims to provide competitive mobile internet access with much more simpler network architecture than it is in normal WCDMA systems
Deployable with existing WCDMA base stations
Utilizes standard 3GPP terminals
Simplified architecture brings many benefits such as
Cost-efficient broadband wireless access
Improves the delay performance
Transmission savings
Enables flat rating for the end user
Works anywhere (compared to WLAN or WIMAX)

49. I-HSPA (2/2) I-HSPA Internet / Intranet NodeB / E-NodeB SGSN GGSN RNCUE
Internet /
Intranet
I-HSPA

50. Conclusions

51. Conclusions (1/2)
High Speed Packet Access evolution for WCDMA was introduced in Release 5 and 6 for downlink and uplink, respectively
HSPA offers much higher peak data rates, reaching in theory up to 14 Mbps in the downlink and 5.4 Mbps in the uplink, in addition to reduced delays
Key technologies with HSPA are
Fast Layer 1 retransmissions i.e. HARQ
Node B scheduling
Shorter frame size (2ms in DL and 2/10ms UL)
Higher order modulation and coding along with link adaptation in downlink
Real support for multicodes in the uplink

52. Conclusions (2/2)
HSPA improved also the performance of delay critical low bit rate services like VoIP even though it was not originally designed for it
Continuous Packet Connectivity (CPC) enhancements introduced in Release 7 improved VoIP performance even more
I-HSPA was introduced to provide competitive internet access solution
High data rates with low delay
Reduced costs => flat rate could be possible
Femtocells were introduced to improve the mobile convergence and performance in small offices or at home, for instance

53. HSPA vs DCH (basic WCDMA)
Feature
DCH
HSUPA
HSDPA
Variable spreading factor
Yes
Yes No
Multicode transmission
Yes (No in practice)
Yes
Yes
Fast power control
Yes
Yes No
Soft handover
Yes
Yes
No (associated DCH only)
Adaptive modulation No No
Yes
BTS based scheduling No
Yes
Yes
Fast L1 HARQ No
Yes
Yes

54. HSPA Peak Data Rates Downlink HSDPA Uplink HSUPA
Theoretical up to 14.4 Mbps
Initial capability 1.8 – 3.6 Mbps
Uplink HSUPA
Theoretical up to 5.76 Mbps
Initial capability 1.46 Mbps
# of codes
Modulation
Max
data rate
# of codes
TTI
Max
data rate
5 codes
QPSK
1.8 Mbps
2 x SF4
2 ms
10 ms
1.46 Mbps
5 codes
16-QAM
3.6 Mbps
2 x SF2
10 ms
2.0 Mbps
10 codes
16-QAM
7.2 Mbps
2 x SF2
2 ms
2.9 Mbps
15 codes
16-QAM
10.1 Mbps
2 x SF2 +
2 x SF4
2 ms
5.76 Mbps
15 codes
16-QAM
14.4 Mbps