Seminar Report

RWTH AACHEN UNIVERSITY

HSPA – High Speed Packet Access Current Trends of Wireless Communications Baimukashev Rashid Matriculation number: 307160 307160

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Content: 1.

Introduction .............................................................................................................................. 3

2.

HSPA – High Speed Packet Access .............................................................................................. 3 1.1

3.

4.

High Speed Downlink Packet Access........................................................................................... 4 3.1.

HSDPA Physical Layer Structure.......................................................................................... 5

3.2.

HS-DSCH Modulation ......................................................................................................... 7

3.3.

HS-DSCH Channel Coding ................................................................................................... 7

3.4.

HSDPA Impact on Radio Access Network Architecture ................................ ........................ 8

3.5.

The Physical Layer Operation Procedure ............................................................................ 9

High Speed Uplink Packet Access ............................................................................................. 10 4.1.

5.

6.

Techniques used in HSUPA ............................................................................................... 10

Evolution HSPA or HSPA+......................................................................................................... 11 5.1.

Advanced receivers .......................................................................................................... 11

5.2.

Mobile Input Mobile Output ............................................................................................ 12

5.3.

Continuous Packet Connectivity ....................................................................................... 12

5.4.

Higher order modulation.................................................................................................. 12

5.5.

Goals of HSPA+................................................................................................................. 13

Recent studies on HSPA ........................................................................................................... 13 6.1.

7.

Deployment of HSPA .......................................................................................................... 4

Release 9 works on HSPA ................................................................................................. 13

Conclusion ............................................................................................................................... 14

References ...................................................................................................................................... 15

HSPA – High Speed Packet Access

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1. Introduction In today’s world the role of wireless communication systems rise significantly. The most rapidly developing is mobile broadband technologies, where phone calls as itself became less crucial, and the data transmission started playing major roles. In my report I would like to discuss the most deployed mobile broadband technology of today’s world – High Speed Packet Access (HSPA), the key new future included in Release 5. This technology provides broadband capacity using resources for voice and other services, hence the data services and multiservice are provided via the same carrier. It leads to the significant increase of the capacity. In the following report at the 2 deployement will be discussed, and then at the 3

rd

nd

chapter the concept and

th

and 4 chapter we will have a look on

HSDPA and HSUPA respectively, particularly on the architecture, structure and implementation. At the 5

th

and 6

th

chapters there will be a brief overview on latest

improvements of HSPA, like HSPA + and DC-HSPA and MC-HSPA.

2. HSPA – High Speed Packet Access The High Speed Packet Access technology is the most widely used mobile broadband technology in communication world. It was already built in more than 3.8 billion connection with GSM family of technologies. The HSPA technology is referred to both High Speed Downlink Packet Access (3GPP Release 5) and to High Speed Uplink Packet Access (3GPP Release 6). The Evolved HSPA technology or HSPA + is the evolution of HSPA that extends operator’s investments before the next generation’s technology 3GPP Long Term Evolution (LTE or 3GPP Release 8). The HSPA technology is implemented on third generation (3G) UMTS/WCDMA network and accepted as the leader in mobile data communication. Using the HSDPA optimization on downlink is performed, whereas the HSUPA technology applying Enhanced Dedicated Channel (E-DCH) sets some improvements for the uplink performance optimization. The products that support HSUPA became available in 2007 and the combination of both HSDPA and HSUPA were called HSPA. Adopting these technologies the throughput, latency and spectral efficiency were improved. Introducing HSPA resulted to the increase of overall throughput approximately to 85 % on the uplink and a rise more than 50 % in user throughput. The HSPA downlink available rates are 1 to 4 Mbps and for the uplink are 500 kbps to 2Mbps as of 1 quarter of 2009. The theoretical bit rates are 14Mbps at the downlink and 5.8 Mbps at the uplink in a 5MHz channel. Besides, the latency is notably reduced as well. In the improved network, the latency is less than 50ms, and after the introduction of 2ms Transmission Time Interval (TTI) latency is expected to be just 30ms.


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HSPA offers an effective wireless broadband technology that can be evolved to HSPA+ to meet the increasing customer demands. HSPA+ implements many of the techniques offered by LTE.

1.1

Deployment of HSPA

As reported by independent analyst firm Informa Telecoms & Media almost 94 % of UMTS/WCDMA operators and 82.8 million customers globally employing HSPA by the end of 2008, and it is expected that the number of customers will increase to 800 million by 2013 [4]. There are more than 265 operators with HSDPA of which 77 have been upgraded to HSPA; in Latin America, there are 47 HSDPA networks in 23 countries (May 2009). It is forecasted that all WCDMA operators will upgrade their network to HSPA.

3. High Speed Downlink Packet Access The main idea of HSDPA concept is a growth of packet access throughput with methods known from Global System for Mobile Communication (GSM)/ Enhanced Data Rates for Global Evolution (EDGE) standards, involving link adaptation and fast physical layers (L1) retransmission combining. The demand of arriving to possible memory requirements and bringing control for link adaptation closer to the air interface brought forward the High Speed Downlink Shared Channel (HS-DSCH). The functioning of HSDPA is done in a way that after calculating the quality of every HSDPA user based for example on power control, ACK/NACK ratio, and HSDPA specific user feedback at the Node-B, then scheduling and link adaptation are immediately conducted depending on the active scheduling algorithm and user prioritization scheme. Using HSDPA the fundamental features of WCDMA like variable spreading factor (SF) and fast power control are switched off and replaced by adaptive modulation and coding (AMC), extensive multicode operation and a fast and spectrally efficient retransmission strategy. The power control dynamics in downlink is 20 dB, and at the uplink it is 70 dB. Due to intra-cell interference (interference between users on pa rallel code channels) and Node-B implementation some limitation are appeared for the downlink dynamics. Consequently, a near to Node-B user’s power is unable to be reduced maximally by the power control. Moreover, the reduced power beyond 20 dB influences a little on the capacity. With HSDPA, this property is handled by the link adaptation function and AMC to choose a coding and modulation combination that demands higher Ec/Io, which is available to the user near to Node-B. This leads to the increase of customer throughput. Utilizing simultaneously up to 15 multicodes in parallel, a large dynamic range of the HSDPA link adaptation and maintenance of a good spectral efficiency are enabled. Using more robust coding, fast Hybrid Automatic Repeat Request (HARQ) and multicode operation makes the variable SF no more necessary.


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In order to profit from the short term variations, the scheduling decisions are performed in the Node-B, so the capacity allocations for one user are done in a short time, in a friendly conditions. The physical layer packet combining is that the terminal accumulates the received data packets in soft memory and in the case of decoding failure, the new transmission is combined with the old one before channel decoding. The retransmission can be the s ame as the first transmission or can be with different bits relatively to the channel encoder output received during the last transmission. With addition incremental strategy, a diversity gain and improving decoding efficiency can be achieved.

3.1.

HSDPA Physical Layer Structure

In the implementation of HSDPA three new channels are introduced in the physical layer specification [1]: 1. High Speed Downlink Shared Channel (HS-DSCH) – the user data in the downlink direction is carried, with up to 10 Mbps peak rate using 16QAM. 2. High Speed Shared Control (HS-SCCH) – the necessary physical control information is carried, so the data on HS-DSCH can be decoded and physical layer of the data sent on HSDSCH in the case of retransmission of erroneous packet can be combined. 3. Uplink High Speed Dedicated Physical Control Channel (HS-DPCCH) – the control information, like ARQ acknowledgements (both negative and positive ones) and feedback information, is carried.

3.1.1. High Speed Downlink Shared Channel (HS-DSCH) In HS-DSCH the shorter 2ms Time Transmission Interval (TTI) or interleaving period has been added to achieve a short round trip delay for the operation between the terminal and NodeB for retransmissions. Introducing 16QAM and lower encoding redundancy raised the instantaneous data peak rate. Besides, the SF is fixed and it always 16, and multicode transmission and code multiplexing of variable users can be done. The maximum code number that can be assigned is 15, however depending on the user equipment capability individual terminal can receive maximum 5, 10, and 15 codes.

3.1.2. High Speed Shared Control Channel (HS-SCCH) At HS-SCCH the information required for HS-DSCH demodulation is carried. The UTRAN needs to allocate a number of HS-SCCHs that correspond to the maximum number of users that will be code-multiplexed. When the data is missing, there is no need of HS-SCCH. Every HS-SCCH consists of three slot duration divided into two functional parts. First part distributes the time-critical information required for demodulation in short time in order to avoid chip level buffering. The second part carries Cyclic Redundancy Check (CRC) and HARQ process information.


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HS-SCCH adopts 128 SF that can accommodate 40 bits per slot. Each part is encoded individually, because the time-critical information must be available immediately after the first slot and thus cannot be interleaved together with the Part 2. The HS-SCCH Part 1 parameters indicate the following: 

Codes to despread.



Modulation to indicate (QPSK or 16QAM)

The Part 2 parameters indicate the following: 

Redundancy proper information



ARQ process number to show which ARQ process the data belongs to



First transmission or retransmission indicator.

Figure 5. HS-SCCH and HS-DSCH timing relationship [1]

3.1.3. Uplink High Speed Dedicated Physical Control Channel (HS-DPCCH) The HS-DPCCH is consists of two parts and carries following information: 

ACK/NACK transmission, reflecting results of the CRC after the packet decoding and combining



Downlink channel quality indicator (CQI) to denote which estimated transport block size, modulation type and number of parallel codes could be received properly (with reasonable BLER) in the downlink direction

Figure 6. HS-SCCH and HS-DSCH timing relationship [1]


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3.2.

HS-DSCH Modulation

16QAM comparing to QPSK doubles the peak data rate and lets up to 10 Mbps peak data rate with 15 codes of spreading factor 16. The HSDSCH capable terminal needs to obtain an estimate of the relative amplitude ratio of the DSCH power level compared to the pilot power level, and this requires that Node B should not adjust the HS-DSCH power between slots if 16 QAM is used in the frame. Otherwise, the performance is degraded as the validity of an amplitude estimate obtained from Common Pilot Channel (CPICH) and estimated power difference between CPICH and HS-DSCH would no longer be valid.

Figure 2. QPSK and 16 QAM constellations

3.3.

HS-DSCH Channel Coding

Due to there is only one transport channel on the HS-DSCH, the multiplexing is not used any more. Besides, there is no intra-frame and inter-frame interleaving. Finally, just turbo coding is used. Varying the block size, the modulation scheme and a number of multicodes code rate range of 0.15-0.98 can be achievable. The key issue is the introduction of the hybrid ARQ (HARQ) functionality.

Figure 3. HS-DSCH channel coding chain [1]


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Figure 4. HARQ function principle [1]

3.4.

HSDPA Impact on Radio A ccess Network Architecture

After the introducing HS-DSCH, extra HSDPA Medium Access Control (MAC) layer is added in the Node-B. This way, all the control can be performed by the Node-B, bringing faster retransmission, and the shorter delays with packet data operation during the retransmission are required. When the relocation is not used the real termination could be several RNC’s further in the network. A flow control mechanism between Node B and RNC is required to make sure that Node-B buffers are used correctly and data loss do not appear due to Node-B buffer overflow. The functionalities of Radio Link Control, such as c ontrolling the retransmission if the HS-DSCH transmission from the Node-B fails after, are still present at the RNC. Despite that the new MAC functionality is introduced in the Node-B, the RNC has still the Release ‘99/Release 4 functionalities. Handling the Automatic Repeat Request functionality, scheduling and priority handling is the main functionality of the new Node-B. In order to ensure the mask for each transmission to be identical enabling physical layer combining of retransmission ciphering is done in the RLC layer.

Figure 1. HSDPA protocol architecture [1]


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3.5.

The Physical Layer Operation Procedure

The steps of the physical layer operation of the HSDPA: 

The scheduler in the Node B estimates the conditions of the channel, the pended data in the buffer, the expired time since the last session of the user and so on.



After defining TTI for the terminal, the HS-DSCH parameters are assigned.



In order to inform the terminal of the necessary parameters, the HS-SCCH two slots are transmitted by the Node-B before the corresponding HS-DSCH TTI.



The given HS-SCCHs are monitored and after the decoding of the Part1 from an HSSCCH determined for that terminal, the rest of the HS-SCCH is decoded and terminal will buffer the necessary codes from the HS-DSCH.



As soon as the HS-SCCH parameters are decoded from Part 2, the terminal can define to which ARQ process the data belongs and the whether it is required the combine of the data and that already in the soft buffer.



After the potentially combined data is decoded, the terminal sends ACK/NACK indicator in the uplink direction.



If the transmission is performed in the same TTI the same HS-SCCH is used.

The timing values for the terminal operation from HS-SCCH reception through HS-DSCH decoding to the uplink ACK/NACK transmission are specified for the HSDPA operation procedure. The 7.5 slots timing value from the end of the HS-DSCH TTI to the start of the ACK/NACK transmission in the HS-DPCCH in the uplink is very crucial.

Figure 7. Terminal timing with respect to one HARQ process [1] Since downlink DCH and uplink DCH have no alignments to the HSDPA transport channels, the uplink HS-DPCCH may start in the middle of the uplink as well, and this needs to be taken into account in the uplink power setting process. The uplink timing is thus quantized to 256 chips and minimum values to 7.5 slots – 128 chips, 7.5 slots + 128 chips.


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Figure 8. Uplink DPCH and HS-SCCH timing relationship [1]

4. High Speed Uplink Packet Access The High Speed Downlink Packet Access (HSUPA) is used for the uplink performance, and introduces Enhanced Dedicated Channel (E-DCH). Networks supporting HSUPA were available since 2007. Higher throughputs, reduced latency, and i ncreased spectral efficiency were achieved applying HSUPA. It is standardized in Release 6. The result is 85 % increase in overall cell throughput on the uplink and more than 50 % gain in user throughput.

4.1.

Techniques used in HSUPA



Introducing Enhanced dedicated physical channel



A short Transmission Time Interval (TTI) 2 milliseconds (ms), enables sharper responses at the case of condition changes of the radio and an error.



Fast Node-B-based scheduling, that allocation of the radio resources is done m ore efficiently by the Node-B



Fast Hybrid Automatic Repeat reQuest (HARQ), which improves the efficiency of error processing.



The combination of TTI, fast scheduling, and fast HARQ also serves to reduce latency, which can benefit many applications as much as improved throughput.

HSUPA as itself is not dependent on a HSDPA and can be implemented separately, however for the better performance of the network it more beneficial applying both techniques at the downlink and uplink. The improved uplink mechanisms also translate to better coverage, and for rural deployments, larger cell s izes. Applying HSUPA different throughput rates on various parameters including spreading factor of the codes, the TTI values, and transport block size of the bites, are achievable.


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HSUPA category

Codes x Spreading

TTI

Transport block size

Data Rate

1 2 2 3 4 4 5 6 6

1 x SF4 2 x SF4 2 x SF4 2 x SF4 2 x SF2 2 x SF2 2 x SF2 2 x SF2 + 2 x SF4 2 x SF2 + 2 x SF4

10 10 2 10 10 2 10 10 2

7296 14592 2919 14592 20000 5837 20000 20000 11520

0.73 Mbps 1.46 Mbps 1.46 Mbps 1.46 Mbps 2 Mbps 2.9 Mbps 2 Mbps 2 Mbps 5.76 Mbps

Table 1. HSUPA Peak Throughput Rates Besides, the latency is decreased notably. After the optimization the latency is reduced to 50 ms, whereas just at HSDPA networks it is 70 ms. And introducing 2 ms TTI, the latency is just 30 ms.

5. Evolution HSPA or HSPA+ High Speed Packet Access plus or Evolution High Speed Packet Access is standardized in 3GPP Release 7 and Release 8. The main idea of developing of HSPA is utilization of available radio technologies and maximizing CDMA-based radio performance. The enhancements for the HSPA + were settled in 3GPP Release 7 and then later in Release 8. The improvements covered advanced receivers, MIMO, Continuous Packet Connectivity, Higher-Order Modulation and one Tunnel Architecture.

5.1. Advanced receivers There are several different types of implementation of receiver designs [5]: 

Type 1, mobile receive diversity



Type 2, channel equalization



Type 3, combination of receive diversity and channel equalization



Type 3i, interference cancellation.

The first approach is mobile receive diversity that enables combination of received signals from separate receiving antennas. Since the combined signal can better decoded it results in doubling of downlink capacity, when synchronized with channel equalization. At higher speeds when inter symbol interference appears due to multipath effect and shortened symbol period, and the advanced-receiver architectures with channel equalizers can be solution for these demands. Advanced receivers should employ interference cancellations and generalized rake receivers (G-Rake).


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5.2.

Mobile Input Mobile Output

The MIMO technology uses both at the transmission and receiving sides multiple antennas and different data streams are sent over different transmitters. Applying MIMO the multipath is solved relying on signals to travel across different uncorrelated communications paths, working on parallel and gaining in throughput.

Figure 9. : MIMO Using Multiple Paths to Boost Throughput and Capacity Relatively to 1x1 antennas, 2x2 MIMO antennas are able to increase cell throughputs up to 80 %. Double Transmit Adaptive Array (D-TxAA) is standardized spatial multiplexing MIMO in Release 7.

5.3.

Continuous Packet Connectivity

In Release 7 the uplink interference is reduced generated by dedicated physical control channels of packet data users when those channels have no user data to transmit. CPC allows both discontinuous uplink transmission and discontinuous downlink reception, where the modem can turn off its receiver after a certain period of HSDPA inactivity. CPC is especially beneficial to VoIP on the uplink, which consumes the most power, because the radio can turn off between VoIP packets.

Figure 10. : Continuous Packet Connectivity

5.4.

Higher order modulation

Another way of increasing the throughput is applying 64QAM on the downlink and 16QAM on the uplink.


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5.5.

Goals of HSPA+



Utilize the full potential of a CDMA before switching to OFDM platform in 3GPP LTE



Approaching to similar performance as LTE in 5 MHz bandwidth



Smooth interworking facilities between LTE and HSPA+



Possibility of packet-only mode for both voice and data



Compatibility with previous generation systems, i.e. HSPA, GSM, EDGE and so forth.



Facilitate migration from current HSPA infrastructure to HSPA+ infrastructure

6. Recent studies on HSPA The big companies like Qualcomm, Ericsson, Nokia/Nokia Siemens Networks, and Huawei in cooperation with 3GPP group put forward recent research studies over HSPA improvements, that resulted into below 3GPP RAN plenary [6]: 

The peak rate improvements of all the features are as expected.



MC-HSDPA and DC-HSUPA provide substantial gains over the combination of single carrier and/or DC-HSDPA operation with the same number of carriers in downlink and dual si ngle carrier HSUPA operation in uplink.



For the studied highly loaded systems (larger number of users) with ful l buffer traffic source models, MC-HSDPA and DC-HSUPA provide gains that are smaller.



In the environments where both the DCHSDPA and single carrier MIMO benefits manifest themselves, both gains are obtainable simultaneously with MIMO + DCH SDPA combination.



MC-HSDPA gains on two separate frequency bands are similar to MC-HSDPA in a single frequency band. Designing the physical layer control channel support for the features does not cause any



significant problems and can be considered to be the same for both single, as well as two separate frequency band cases. Implementation complexity of the base-band processing is expected to increase linearly



with the peak rate. 

The number of new UE categories needed would depend on the number of all owed combinations of the different features and allowed band combinations.

6.1.

Release 9 works on HSPA

Concerning HSPA in 3GPP Release 9 were introduced three new work items.

6.1.1.

Support for different bands for Dual-Cell HSDPA

This work gives opportunity for paired cells of DC-DSDPA to be operated on two different bands, whereas in Release 8 they could work just on adjacent carriers. The two cells will belong to the same Node-B and the mobility is based one of the carriers only (anchor carriers).


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6.1.2.

Combination of DC-HSDPA with MIMO

There just few scenarios that are possible, carriers must be from the same Node-B and must be adjacent to each other. Moreover, the dual carrier transmission will only apply to HSDPA physical channels. A MIMO support in combination with DC-HSDPA will allow operators deploying Release 7 MIMO to benefit from the DC-HSPDA functionality as defined in Release 8.

6.1.3. Dual Cell HSUPA There just few scenarios as well, carriers are from the same Node-B and have to be adjacent carriers. Furthermore, at least 2 carriers are tuned that minimum 2 carriers are configured simultaneously in the downlink and have the same duplex distance to the uplink.

7. Conclusion HSPA technology is a good solution for the smooth migration from WCDMA to LTE technologies. Introducing it into current UMTS networks it brings up better broadband data service, in which each user can achieve more than 4Mbps in the downlink and exceed 1Mbps in the uplink connections. As the result of introducing shorter Transmission Time Interval the latency is reduced from 70 ms to 30 ms. Besides, employing Evolution HSPA or HSPA + even better performance is achieved. After utilizing MIMO advanced techniques, better modulation schemes as 64QAM

and

introducing Continuous Packet Connectivity data rates up to 42 Mbps in the downlink and 11.5 Mbps in the uplink are achievable. Further findings that were standardized in 3GPP Release 9, improvements of HSPA+ introduced DC-HSPA and MC-HSDPA that gives similar to LTE performance. With the increase of multimedia content, messaging and rapid impact of Internet into our lives the mobility and high data rates started being as the most actual demands of world of today. The High Speed Packet Access is the excellent solution and can be implemented without major impact on the core of the network.


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References 1) Holma, H., Toskala, A. WCDMA for UMTS. Radio access for third generation mobile communications. West Sussex: John Wiley & Sons, 2004. 2) Juha Karhonen, Introduction to 3G Mobile Communications, Artech House, 2003 3) http://www.3gamericas.org/index.cfm?fuseaction=page§ionid=247 4) EDGE, HSPA, LTE: Broadband Innovation, September 2008, 3G Americas, RYSAVY Research 5) David Maidment, Understanding HSDPA's Implementation Challenges, picoChip Designs, 2005 http://www.eetimes.com/design/embedded-internet-design/4009356/UnderstandingHSDPA-s-Implementation-Challenges 6) Eiko Seidel, Standartization updates on HSPA Evolution, Nomor Research GmbH, Munich, Germany, 2009


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