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HSPA systems Kari Aho Senior Research Scientist
2 © 2008 Magister Solutions Ltd Disclaimer Effort has been put to make these slides as correct as possible, however it is still suggested that reader confirms the latest information from official sources like 3GPP specs (http://www.3gpp.org/Specification-Numbering)http://www.3gpp.org/Specification-Numbering Material represents the views and opinions of the author and not necessarily the views of their employers Use/reproduction of this material is forbidden without a permission from the author
3 © 2008 Magister Solutions Ltd Readings related to the subject General readings WCDMA for UMTS – H. Holma, A. Toskala HSDPA/HSUPA for UMTS – H. Holma, A. Toskala 3G Evolution - HSPA and LTE for Mobile Broadband - E. Dahlman, S. Parkvall, J. Sköld and P. Beming, Network planning oriented Radio Network Planning and Optimisation for UMTS – J. Laiho, A. Wacker, T. Novosad UMTS Radio Network Planning, Optimization and QoS Management For Practical Engineering Tasks – J. Lempiäinen, M. Manninen
4 © 2008 Magister Solutions Ltd Contents Introduction HSDPA HSUPA Continuous Packet Connectivity I-HSPA Conclusions
5 © 2008 Magister Solutions Ltd Introduction
6 © 2008 Magister Solutions Ltd High Speed Packet Access (1/3) 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
7 © 2008 Magister Solutions Ltd High Speed Packet Access (2/3) 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
8 © 2008 Magister Solutions Ltd High Speed Packet Access (3/3) 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
9 © 2008 Magister Solutions Ltd WCDMA Background and Evolution GPP Rel /99 3GPP Rel 4 03/01 3GPP Rel 5 (HSDPA) 03/02 3GPP Rel 6 (HSUPA) 2H/04 3GPP Rel 7 HSPA+ 06/07 Further Releases, (LTE) Japan Europe (pre- commercial) Europe (commercial) HSDPA (commercial) HSUPA (commercial)
10 © 2008 Magister Solutions Ltd Questions Why were the packet data capabilities of WCDMA improved even further? For what kind of services was HSPA originally designed?
11 © 2008 Magister Solutions Ltd High Speed Downlink Packet Access (HSDPA)
12 © 2008 Magister Solutions Ltd 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 DSCH was removed due to lack of interest for implementing it in practical networks
13 © 2008 Magister Solutions Ltd 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
14 © 2008 Magister Solutions Ltd HSDPA channels (1/2) 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)
15 © 2008 Magister Solutions Ltd HSDPA channels (2/2) 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) Control information is sent on High Speed Common Control Channel (HS-SCCH) 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
16 © 2008 Magister Solutions Ltd Questions Mention at least purpose to which Rel’99 DCH is used with HSDPA What kind of handovers are supported with HSDPA?
17 © 2008 Magister Solutions Ltd Link Adaptation (1/3) UE informs the Node B regularly of its channel quality by CQI messages (Channel Quality Indicator)
18 © 2008 Magister Solutions Ltd Link Adaptation (2/3) Adaptive modulation and higher order modulation (16/64QAM) with HSDPA Link adaptation adjusts the mode within few ms based on CQI
19 © 2008 Magister Solutions Ltd 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
20 © 2008 Magister Solutions Ltd Fast Retransmissions (1/3) Radio Link Control (RLC) layer ACK/NACKs also possible with HSPA Packet RLC ACK/NACK Retransmisson Packet Layer 1 ACK/NACK Retransmisson Rel ‘99 HSPA RNC NodeB UE
21 © 2008 Magister Solutions Ltd Fast Retransmissions (2/3) RNC NodeB UE User data RLC MAC-d Layer1 MAC-hs HARQ (N)ACK (Re)transmission RLC (N)ACK (Re)transmission
22 © 2008 Magister Solutions Ltd 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)
23 © 2008 Magister Solutions Ltd Questions What is CQI? What does link adaptation do? Which entity initiates RLC re-transmissions? Which entity initiates HARQ re-transmissions?
24 © 2008 Magister Solutions Ltd 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
25 © 2008 Magister Solutions Ltd 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
26 © 2008 Magister Solutions Ltd 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
27 © 2008 Magister Solutions Ltd 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
28 © 2008 Magister Solutions Ltd 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
29 © 2008 Magister Solutions Ltd 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
30 © 2008 Magister Solutions Ltd 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 DCH Node B, Serving HSDPA UE Node B, Part of DCH active set HS-SCCH DCH/HSDPA DCH
31 © 2008 Magister Solutions Ltd 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
32 © 2008 Magister Solutions Ltd 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
33 © 2008 Magister Solutions Ltd Questions How does Round Robin allocate resources for the users? How intra- and inter-Node B handovers differ from each other?
34 © 2008 Magister Solutions Ltd High Speed Uplink Packet Access (HSUPA)
35 © 2008 Magister Solutions Ltd 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
36 © 2008 Magister Solutions Ltd 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.
37 © 2008 Magister Solutions Ltd 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
38 © 2008 Magister Solutions Ltd 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
39 © 2008 Magister Solutions Ltd 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)
40 © 2008 Magister Solutions Ltd HSUPA channels (4/4) NodeB UE E-RGGH E-AGCH E-HICH DPCCH E-DPCCH E-DPDCH
41 © 2008 Magister Solutions Ltd Questions What new features on top of multicodes and shorter frame sizes do HSUPA offer? Is DCH part of the HSUPA?
42 © 2008 Magister Solutions Ltd 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
43 © 2008 Magister Solutions Ltd 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
44 © 2008 Magister Solutions Ltd 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
45 © 2008 Magister Solutions Ltd 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
46 © 2008 Magister Solutions Ltd 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
47 © 2008 Magister Solutions Ltd Questions What is the shared resource in the uplink if power is in the downlink? What kind of scheduling possibilities HSUPA offer?
48 © 2008 Magister Solutions Ltd 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
49 © 2008 Magister Solutions Ltd 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 BLER target which leads to lower power requirement for corresponding data rate
50 © 2008 Magister Solutions Ltd 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
51 © 2008 Magister Solutions Ltd Mobility with HSUPA (2/2) Data Layer 1 ACK/NACK RNC NodeB UE NodeB Layer 1 ACK/NACK Correctly received packet Packet reordering
52 © 2008 Magister Solutions Ltd Questions Why does not DCH support multicodes in practice? If UE is in a two-way soft handover how does the HARQ operate?
53 © 2008 Magister Solutions Ltd Continuous Packet Connectivity (CPC)
54 © 2008 Magister Solutions Ltd 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
55 © 2008 Magister Solutions Ltd 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
56 © 2008 Magister Solutions Ltd Continuous Packet Connectivity (3/5) = DPDCH (DCH) / E-DPDCH (E-DCH) = DPCCH E-DCH with 2-ms TTI (Rel-6, phase 2, VoIP) E-DCH with 10-ms TTI (Rel’6, phase 1, VoIP) R99 DCH with 20-ms TTI (Rel’99, CS voice) 12.2 kbps DCH 32 kbps E-DCH 160 kbps E-DCH Power offset E-DCH with 2 ms TTI and UL DPCCH gating (Rel-7, VoIP) 160 kbps E-DCH PO
57 © 2008 Magister Solutions Ltd 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
58 © 2008 Magister Solutions Ltd 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
59 © 2008 Magister Solutions Ltd VoIP performance with and without CPC In general major performance enhancements visible if circuit switched voice over WCDMA and VoIP over HSPA Rel 7 is compared With Rel 99 CS voice capacity users/cell With Rel 7 VoIP capacity goes beyond 120 users/cell H. Holma, M. Kuusela, E. Malkamäki, K. Ranta-aho, C. Tao: “VoIP over HSPA with 3GPP Release 7”, PIMRC, 2006.
60 © 2008 Magister Solutions Ltd Internet HSPA (I-HSPA)
61 © 2008 Magister Solutions Ltd I-HSPA (1/3) 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)
62 © 2008 Magister Solutions Ltd I-HSPA (2/3) UE NodeB / E-NodeB RNC SGSN GGSN Internet / Intranet Internet / Intranet I-HSPA
63 © 2008 Magister Solutions Ltd I-HSPA (3/3) Round trip time of 32-Byte packet Today HSDPA HSDPA+HSUPA Release 99 ~200 ms HSDPA <100 ms HSUPA ~50 ms Internet Iu + core RNC Iub Node B AI UE I-HSDPA+ I-HSUPA I-HSPA ~25 ms
64 © 2008 Magister Solutions Ltd Conclusions
65 © 2008 Magister Solutions Ltd 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
66 © 2008 Magister Solutions Ltd 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
67 © 2008 Magister Solutions Ltd HSPA vs DCH (basic WCDMA) Feature Variable spreading factor Fast power control Adaptive modulation BTS based scheduling DCH Yes No HSUPA Yes No Yes Fast L1 HARQNoYes HSDPA No Yes Multicode transmission Yes (No in practice) Yes Soft handoverYes No (associated DCH only)
68 © 2008 Magister Solutions Ltd 5 codesQPSK # of codesModulation 5 codes16-QAM 10 codes16-QAM 15 codes16-QAM 15 codes16-QAM 1.8 Mbps Max data rate 3.6 Mbps 7.2 Mbps 10.1 Mbps 14.4 Mbps 2 x SF4 2 ms 10 ms # of codesTTI 2 x SF210 ms 2 x SF22 ms 2 x SF2 + 2 x SF4 2 ms 1.46 Mbps Max data rate 2.0 Mbps 2.9 Mbps 5.76 Mbps Downlink HSDPA 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 HSPA Peak Data Rates
69 © 2008 Magister Solutions Ltd Thank you!
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