High Speed Downlink Packet Access (HSDPA)

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High Speed Downlink Packet Access (HSDPA)


The title for the report is High Speed Downlink Packet Access (HSDPA). Internet is become apart of our every day life and mobile users demand for high speed access while they are on the move. HSDPA can fulfil these demands and offer more services which are broadband related. The report will analyse and evaluate the HSDPA technology, which include the architecture, protocols and protocol status. Also the report discuss HSDPA principle operation and the physical and MAC layer. With Small scale simulation, HSDPA performance and how it handle different types of traffic and users, will be analyse. Also the report will discuss the outlook market and how it compete with other similar technologies in the coming years. By the end of my report I will gain more knowledge and understanding of HSDPA technology and how much mobile users and business can benefit from it.


AES Advance Encryption Standard

AMC Adaptive Modulation and Coding

BTS Base Transceiver Station

DCH Dedicated Channel

DES Data Encryption Standard

DTX Discontinuous Transmission

DSL Digital Subscriber Line

FACH Fast Access Channel

GSM Global System for Mobile Communication

UMTS Universal Mobile Telecommunication System

3G Third Generation

WCDMA Wideband code Division Multiple Access

HSDPA High Speed Downlink Packet Access

HSPA High Speed Packet Access

EDGE Enhanced Data Rate for Global Evolution

HS-DSCH High-speed Downlink Shared Channel

VoIP Voice over IP

TTI Transmission Time Interval

HARQ Hybrid Automatic Response request

RRM Radio resource Management

SRNC Serving Radio Network Controller

RNC Radio Network Controller

RRC Radio Resource Control

PDCP Packet Data Convergence Protocol

RCL Radio Link Layer

MAC Medium Access Control

RACH Random Access Channel

S-CCPCH Secondary Common Control Physical Channel

HS-DSCH High Speed Downlink Shared Channel

HS-DPCCH High-speed dedicated Physical Control Channel

F-DPCH Fractional Dedicated Physical Channel

HS-PDSCH High-speed physical downlink shared channel

EAPOL Extensible Authentication Protocol over LANs

WEP Wired Equivalent Privacy

EAP Extensible Authentication Protocol

RSNA Robust Security Network Association

QoS Quality of Service

1.0 Introduction

Universal Mobile Telecommunication System (UMTS) is most growing mobile technology in the recent years. Resulting of that growing of number of services such as mobile TV, Multimedia and online games video and video streaming, which will demand a high speed data rate. Current 2.5G and 3G service providers are reporting that a large proportion of usage is due to data, and the demand for the high speed data rate will increase specially for multimedia services. Recent Release 99 WCDMA has a maximum of 384 kbps data rate, which will be increased to 512 kbps and beyond. Then the introduction of High Speed Downlink Packet Access (HSDPA), which will boost WCDMA speed and performance. HSDPA has better throughput than WCDMA and it has a higher data rate.

HSDPA is defers from W-CDMA, it uses a high-speed downlink shared channel ( HS-DSCH), which has faster downlink speed, carrying data to mobile phones.

High Speed Downlink Packet Access is mobile communications protocol, based on, and leveraging technologies from the existing W-CDMA protocol. HSDPA aims to bring high-speed data communication speeds more inline with those of standard consumer broadband services.

Implementation of HSDPA can be done in the existing UMTS networks and it can work a long side the 3G networks based on the 3GPP Release 99. there is no need of changing the 3G's core network as long as it can handle HSDPA traffic.

HSDPA sometimes referred to as 3.5G, will be able to offer theoretical download speeds of approximately 1.8Mbps, and upload speeds of 384Mbps. higher communication speeds will soon be possible with advances in technology. Comparable 3G data communications devices.

HSDPA provides a significant increase in high speed mobile communications from its predecessor.

HSDPA modules can now be easily implemented in mobile computers, using either a PC-Card or internal mini-card device. So designing the technology into a mobile computer is not difficult for the manufacturer. The high speed communications of HSDPA allows for a much richer Internet experience for the mobile user. High speed transmission of Video and voice can be transmitted at higher speeds with little loss of quality.

This also opens up mobile Voice Over IP (VoIP) to the consumer. Sending Voice over an Internet connection is certainly cheaper than making a long distance call, and is sure to be the future method of mobile communications as service providers look to implement these solutions for their customers.

The mobile workforce (travelling sales people, international business executives) is the obvious beneficiary of such technologies, but HSDPA can have significant benefits for other users too. HSDPA provides high speed broadband access foe users and business remote locations who may not have access to traditional broadband access methods.

HSDPA uses a number of new techniques which provide a good improvement in performance for mobile users and service providers.

2.0 HSDPA architecture

2.1 Radio resource Management (RRM)

In HSDPA the scheduling control has been moved to BTS and that has overall change in RRM architecture. SRNC has control of handover, which is simplified in the sense that there is no soft handover for HSDPA data. Then there is no need to run user data over multiple Iub and Iur interferences, even the utilization of the Iur interference can be avoided by performing SRNC relocation, when the serving HS-DSCH cell under different controlling RNC.

2.2 Protocol architecture

The protocol architecture can be define as user plane part, which handle all user data, and control plane part.

* Radio Resource Control (RRC) layer handles all the signalling related to configuring the channels, mobility management, etc.

* PDCP is the Packet Data Convergence Protocol, has as its main functionality header compression which is not relevant for circuit-switched services.

* Radio Link Layer (RCL) handles the segmentation and retransmission for both user and control data.

· Medium Access Control (MAC) handles all mapping between the logical channels and the priorities, as well as selection of the data rates being used.

2.3 Protocol states with HSDPA

* Cell_DCH is the state which is used when active data transmission to and from the terminal on the DCH or HSDPA is possible.

* Cell_FACH state, which data can be transmitted in this state, using FACH for the downlink and RACH in the uplink, which means limited data rates these channels do not offer any performance enhancement features of HSDPA.

* Cell_PCH / URA_PCH state, these states are the most efficient ones from the terminal battery consumption point of view.

3.0 HSDPA Principles

HSDPA uses a number of new technologies which aiming to increase capacity and throughput and improve the overall system efficiency.

3.1 HSDPA Technologies

In Release 99 Specifications there are three different methods for downlink packet data operation:

The FACH is used to carry the signalling when the terminal has moved due to inactivity. It is operated on its own and depending on the terminal is in. FACH is decoded either continuously or based on the paging message. For the FACH there neither fast power control nor soft handover. FACH is carried on the secondary common control physical channel (S-CCPCH) with fixed spreading factor.

The DCH has fixed a spreading factor in the downlink with fixed allocation during the connection. It can be used for any kind of service. HSDPA is always operated with the DCH running in parallel.

HSDPA introduced new channels (HS-DSCH) for user data and (HS-SCCH) in the downlink and (HS-DPCCH) in the uplink. Also in Release 6 specification there is a new channel called fractional dedicated physical channel (F-DPCH), which cover for operation when all downlink traffic is carried on the HS-DSCH.

The general HSDPA operation principle is shown in below, where Node B estimates the channel quality of each active HSDPA user on the basis of the physical layer feedback received in the uplink. Scheduling and link adaptation are then conducted at a fast pace depending on the scheduling algorithm and user prioritization scheme.

The other key new technology is physical layer retransmission. The packet is received in the buffer in the BTS and kept there, if there any packet decoding failure, retransmission automatically takes place from the base station without RNC involvement.

3.1.1 High-speed downlink shared channel (HS-DSCH)

HS-DSCH is defined as a transport channel which carries the user data in HSDPA. Its has 2 ms TTI, which help to reduce round trip delay between UE and Node B. this allow a UE to have minimal steady level of data rate all the time. In the physical layer HS-DSCH is mapped to high-speed physical downlink shared channel (HS-PDSCH). HS-DSCH has the flowing properties:

* Link adaptation and the use of different coding and modulation.

* Support of higher order modulation.

* User allocation with BTS based scheduling every 2 ms, with fast physical layer signalling.

* Use of physical layer retransmissions and retransmission combining.

* Multimode operation with fixed spreading factor, only SF 16 is used.

* Use of turbo-coding

* No discontinuous transmission (DTX)

3.1.2 Higher Order Modulation

Beside QPSK modulation, HSDPA uses 16QAM modulation which allow 4 bits can be carried per symbol, instead of 2 bits per symbol with QPSK modulation. This mean with

higher order modulation we can send more data on a single channel

3.1.3 Fast Link Adaptation

HSDPA uses fast link adaptation to vary the amount of coding error generated by radio channel coding scheme. This is done by changing and varying the coding and modulation according to link or channel condition, which will improve data rate and signal quality.

3.1.4 Hybrid Automatic Repeat Request

3.2.1 HS-DSCH coding

HS-DSCH use only turbo-coding. The channel coding chain is simplified and only transport channel active at a time. An additional new issue is the handling of 16QAM and the resulting varying number of bits carried by the physical channel even the number of codes used remains fixed.

3.3 High-speed shared control channel (HS-SCCH)

HS-SCCH carries time-critical signalling information which allows the terminal to demodulate the correct codes. There are no pilots or power control bits on the HS-SCCH, so the phase reference is always the same as for the HS-DSCH. HS-SCCH is divided into two parts:

* The first part carries information needed to enable de-spreading of the correct code and contains the modulation information.

* The second part contains less urgent information, such as which ARQ process is being transmitted.

3.4 High-speed dedicated physical control channel (HS-DPCCH)

HS-DPCCH carries the uplink feedback information from the terminal to the BTS to enable the link adaptation and physical layer retransmissions. It has fixed spreading factor of 256 and 2 ms / three-slot structure. HS-DPCCH operation has been enhanced in release 6 to improve cell edge operation.

3.4.1 Fractional DPCH (F-DPCH)

F-DPCH is a stripped-down version of DPCH that handle the power control. The code resource is time-shared and several users can share the same code space for power control information. It has some restrictions: not usable with services requiring data to be mapped to the DCH, feedback-based transmit diversity is not usable.

3.4.2 HS-DSCH Link adaptation

Link adaptation is very dynamic as it operates with 2 ms granularity with the HS-DSCH. It is based on physical layer CQI being provided by the terminal. By using link adaptation, the network will gain from the limitation of power control dynamics in the downlink.

3.4.3 Physical layer operation

HSDPA physical layer operation goes through the following steps once one or more users have been cond as using the HS-DSCH and data start to reach the buffer in the Node B.

* Node B evaluate channel condition, buffer status, time from last transmission, transmission pending and so forth for each user every 2 ms.

* The Node B identifies the necessary HS-DSCH parameters, including number of codes, 16QAM usability and terminal capability limitations.

* The Node B starts to transmit the HS-SCCH two slots before the corresponding HS-DSCH TTI.

* The terminal monitors the terminal-specific set of at most four HS-SCCHs given by the network. Once the terminal has decoded Part 1 from an HS-SCCH, it will start to decode the remaining parts and will buffer the necessary codes from the HS-DSCH.

* After decoding the HS-SCCH parameters from Part 2, the terminal can determine to which ARQ process the data belong and whether they need to be combined with data already in the soft buffer.

* In the Release 6 version, a pre-amble is sent in the ACK/NACK field if the feature is cond to be used by the network.

* Upon decoding the potentially combined data, the terminal sends in the uplink direction an ACK/NACK indicator, depending on the outcome of the CRC conducted on the HS-DSCH data.

* If the network continues to transmit data for the same terminal in consecutive TTIs, the terminal will stay on the same HS-SCCH that was used during the pervious TTI.

* In Release 6, when the data flow end, the terminal sends a post-amble in the ACK/NACK field.

HSDPA basic features

1) Adaptive Coding and Modulation

The principle of ACM is to alter the coding and modulation for transmission according to the condition of the receiver channel.

2) Hybrid Automatic Repeat Request (HARQ)

When receiver can not decode data because of data error, HARQ main job is retransmitting the data.

3) The Active time Space Priority (TSP)

TSP manage and control packets in the buffer of base station.

3.0 HSDPA Performance

HSDPA has a high data rate of 10 Mbit/s in normal 5 MHz channel, also its fast switching capability (2 ms) increases trunking efficiency for high data rate packet service. HSDPA high order modulation can be used to increase user throughput and improve cell capacity. Also fast packet scheduling gives a high cell capacity and maintain required QoS.

There are several factors that effect HSDPA performance and here some of them:

* Network algorithms, specific algorithms such as MAC-hs packet scheduler, HS-DSCH link adaptation, HS-SCCH power control and HSDPA transmission resource allocation.

* UE detector performance and capability, such as peak data rate, number of HS-PDSCH channel codes, number of transmit and receive antennas, and baseband receiver algorithms.

* Traffic and quality of service (QoS), such as number of active users, and their corresponding QoS requirements.

* Channel condition which include the environment of the cell itself, time dispersion, own cell interference and other cell inference.

3.1 Single-user Performance

QPSK (Quarter phase shift keying) modulation is used when is only one HS-PDSCH code is used, so there is less power required per user bit and the result is low data rate. Other factors that effect single-user performance are transmission, processing delays and the Channel Quality Indicator (CQI). Indoor user with microcell in use, channel quality will be good and so the data rate, because of less time dispersion and interference. In the other hand, outdoor user using macro cell, and because of high time dispersion and other cell interference, peak data rate is limited. Data coverage is low because there is no switching gain in single user situation, but overall cell capacity has a gain from soft handover.

3.2 Multiple-user Performance

The use of fast packet scheduling, in multiple user environments, has a great effect on the cell throughput and the required QoS by the end user. The throughput gain directly related to the number of users using the same HS-DSCH channel and the interference ratio. Note that when the of users increase, per user throughput decreases because HS-DSCH capacity is shared between users.

HSDPA uses different types of scheduling methods and here are some of them;

* Round robin and fair packet scheduler; this method dose not take count of channel condition and schedule users the best instantaneous channel quality.

* Proportional fair algorithm which offers an attractive trade off between user fairness and cell capacity, and used when users have good instantaneous channel condition. The method improve user and cell throughput [1].

4 HSDPA vs. WiMax

4.1 Coverage and bit rates

WiMAX range coverage can reach up to 50 km, with bandwidth up to 70 Mbit/s, but the actual bandwidth is lower than the above and still subject to debate. WiBro has a data rate up to 30 Mbit/s, which gives users downlink data rate up to 18 Mbit/s and 6 Mbit/s on the uplink. But signal is getting weaker when distance between UE and BTS is large, because the signal over noise ratio is decrease quicker as distance increase. Also WiMAX BTS's can communicate with each other even without line of sight.

In HSDPA system, downlink bandwidth can reach up to 14.4 Mbps at distance less than 1km, and 384 kbit/s on the uplink, but bandwidth drop as distance increase, same as in WiMAX system. but users can transmit data even with very low bandwidth.

4.2 Capacity

HSDPA technology is design for simultaneous users, lots users can share channels and bandwidth. If number of users increase, the system can still cope but with low data rate.

WiMAX can only operate with few dozens of users and the network can not cope when number of users increase.

4.3 Multimedia capability

For both HSDPA and WiMAX, there is similarities in multimedia capability and capacity and both have QoS multimedia applications.

4.4 Security features

HSDPA authenticate users through their SIM card which include two way challenge, encryption of signalling traffic, use of two way authentication of 3G network and encryption on radio link. and does not have any other security feature. Data encoding for different users, typical of all CDMA standards, works better than any cryptographic algorithm, but not if an intruder is in a base station or somehow gets its channels code. WiMAX supports modern cryptographic algorithms, such as AES and DES. It uses X.509 certificate and EAP. It will certainly please corporate users, who want to keep their data in secret.

Mobile WiMAX


Date of introduction



Downlink data rate (max)

23 Mbit/s

14.4 Mbit/s

Uplink data rate (max)

4 Mbit/s

384 kbit/s


50 ms

100 ms


Certificate or EAP

SIM-based security


2.3 GHz, new at 2.5 GHz

3G 2 GHz, new at 2.5 GHz

Service set-up time

50 ms

2 sec reducing to 0.6 esc

Table: Comparison of WiMAX and HSDPA (BT Technology Journal [6])

5 Market Outlook for HSDPA

Internet market is growing rapidly, in recent years, specially mobile broadband, which provide internet for users either on the move or in remote areas where they can not get access to traditional broadband access. In 2009, more than 250 HSDPA networks went online providing broadband services across the globe, with speed up to 42Mbit/s. the number of broadband subscribers are increasing rapidly, and by end of year 2013 the total subscribers will be more than 30% of whole mobile users.

The implementation of HSDPA does not require building a new network infrastructure, it can be done with existing 3G network with better coverage and very effective and efficient use of bandwidth. So rolling out HSDPA services can done quickly and cost effectively driven by users demand for such service.

PC card are the first HSDPA device, it can be slotted into desktop or laptop giving users high speed internet broadband connection. Then it moved on to USB modems, and now laptop and mobile phones come with built in HSDPA capability. Also HSDPA service can be provided through landline Ethernet and Wi-Fi.

5.1 UK Market

The introduction of mobile broadband services is enabled by HSDPA technology in 3G mobile networks, that enables laptop uses to access the Internet on the move at speeds of up to 1.8 Mbit/s, similar to ADSL and cable modem broadband services. Vodafone was the first UK Mobile Operator to lunch HSDPA service in 2006, which offer subscriber mobile broadband with speed up 2Mbps and monthly fee of £45, with maximum usage of one Gbyte per month. Now all operators in the UK are offering HSDPA service with average price of £10 to £15 a month and maximum download of 2 Gbyte. That mean subscribers are paying average of £0.025 per Mb. Also some operators are offering free WiFi usage.

Now, Vodafone offering mobile broadband with maximum speed of 8Mb, and working in upgrading its network to maximum speed of 14.4 Mb. This will make Vodafone the first operator to offer highest downlink speed, but in real life this speed will never be true. Other UK operators are offering a lower speed, T Mobile offering mobile broadband with speed up to 4.5Mbp/s, O2, Orange and Three are offering speed of up 3.6Mbp/s and they are still working to upgrade their network to accommodate speed of 7Mbp/s.

5.2 International Market

HSDPA can be implemented on 3G networks and there no need for building new infrastructure, this make of rolling out HSDPA a head of its competitor. Number of subscribers are reach the 1 Billion in commercial HSPA enabled networks, with number of 204 HSDPA operator in 89 countries, has been reported. With 35 networks in APAC region, 61 networks in Western Europe, 34 networks in Eastern Europe, 16 networks in the USA and Caribbean and 20 networks in Middle East and Africa [7].

6 Conclusion

HSDPA is the new generation in the mobile broadband technology, which has a higher data rate and faster internet access. HSDPA dose not require building a new networks and it can be implemented on the existing 3G networks. Mobile operators still working hard and promise their customers to upgrade their networks to top maximum downlink speed of 14.4Mbit/s, while keeping their prices down. But HSDPA facing a big competition from similar technologies such as WiMAX, which offer maximum downlink speed up to 23Mbit/s. HSDPA has a good mobility, voice and data from cellular platform.

7 References

1 Harri Holma and Antti Toskala, WCDMA for UMTS: HSPA Evolution and LTE, fourth edition, Wiley 2007

2 Harri Holma and Antti Toskala, HSDPA/HSUPA for UMTS: High Speed Radio Access for Mobile Communications, Wiley 2006

3 Byeong Gi Lee and Sunghyun, “Broadband Wireless Access and Local Networks: Mobile WiMAX and WiFi, Artech House 2008

4 Nokia HSDPA Solution, [online], visited on 28/2/10, available at http://nds2.ir.nokia.com/NOKIA_COM_1/About_Nokia/Press/WhitePapers/pdf_files/HSDPA

5 WCDMA and WLAN for 3G and beyond, [online], visited on 1/3/10, available at http://ieeexplore.ieee.org/Xplore/login.jsp?url=http%3A%2F%2Fieeexplore.ieee.org%2Fstamp%2Fstamp.jsp%3Ftp%3D%26arnumber%3D998520%26isnumber%3D21543&authDecision=-203

6 N Johnston and H Aghvami, comparing WiMAX and HSDPA, a guide to the technology, BT Technology Journal, Vol. 25 No. 2 April 2007.

7 HSPA is Global system of choice for mobile broadband, GSA survey, [online], visted on 3/3/10, available at http://www.mobileeurope.co.uk/news_wire/113504/GSA_survey_said_to_confirm_HSPA_as_global_system_of_choice_for_mobile_broadband.html