HSDPA
INTRODUCTION
3G HSDPA High Speed Downlink Packet Access is an upgrade to the original
3G UMTS cellular system (3.5G) that provides a much greater download speeds for
data. With more data being transferred across the downlink than the uplink for data-
centric applications, the upgrade to the downlink was seen as a major priority.
Accordingly 3G UMTS HSDPA was introduced into the 3GPP standards as soon as
was reasonably possible, the uplink upgrades following on slightly later.3G UMTS
HSDPA significantly upgrades the download speeds available, bring mobile
broadband to the standards expected by users. With more users than ever using
cellular technology for emails, Internet connectivity and many other applications,
HSDPA provides the performance that is necessary to make this viable for the
majority of users.
When HSDPA will be implemented, it can coexist on the same carrier as the
current Release’99 WCDMA services. This will enable a smooth and cost-efficient
introduction of HSDPA into the existing WCDMA networks. The driving force for
high data rates are greater speed, shorter delays when downloading audio, video and
large files which will be used in PDA’s, smart phones etc. Further a user can
download packet data over HSDPA, while at the same time having a speech call.
HSDPA offers theoretical peak rates of up to 10MBps and in practice more than
2MBps. The technical aspects behind the HSDPA concept include the following:
1. Shared channel transmission
2. Adaptive Modulation and Coding (AMC)
3. Fast Hybrid Automatic Repeat Request (H-ARQ)
4. Fair and fast scheduling at Node B
5. Fast cell site selection (FCSS)
6. Short transmission time interval (TTI)
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EVOLUTION OF HSDPA
The second generation (2G) of mobile cellular systems has been developed as
a successor of analogue systems (called 1G) and became a commercial success in the
middle 90's. 2G systems cover a certain number of different technologies among
which the most important are: (1) Global System for Mobile Communications (GSM),
the more developed technology in the world, in Europe, in many African, Asian and
Middle-East countries, and also in American countries (USA, Canada and a lot of
South America countries), (2) cdmaOne (also called IS-95), mainly used in the
America and Asia-Pacific regions, (3) IS-136 (TDMA, also called D-AMPS), used in
North and South America and (4) Personal Digital Cellular (PDC), used only in
Japan. These systems offer circuit switched voice and rather limited data rate (e.g. 9.6
Kbps for GSM circuit mode), which nevertheless opened a new market for mobile
data communications through the Short Message Service (SMS).
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The demand for higher data rates has led to the development of so-called
"2G+" or "2.5G" systems. For the GSM technology, the first step has been General
Packet Radio Service (GPRS) which offers packet switched transmission at bit rates
of about 40 kb/s by allocating several time slots of a frame to the same data
transmission. The second step for GSM has been Enhanced Data rates for GSM
Evolution (EDGE), which mainly consists in the introduction of the 8-PSK
modulation, multiplying by 3 the on-line date rate compared to GPRS. Indeed, EDGE
is included in the 3G – IMT-2000 family of systems. IS-95 and IS-136 have also
evolved in the same direction. IS-95-HDR implements a packet mode at 144 kb/s
(first step towards CDMA2000), while IS-136 has evolved to an EDGE-GSM-based
system under the name of Universal Wireless Communications 136 (UWC-136).
These technical evolutions aiming to provide more and more efficient data services
have paved the way for the definition of 3G systems.
The ITU has deployed a lot of efforts to define a family of systems, called 3G
systems, which provide high data rate to offer multimedia services. Under the name
International Mobile Telecommunications 2000 (IMT-2000), these systems have been
designed for use in the frequency bands selected by the World Radio Conference
(WRC) in the year 1992. The IMT-2000 family is composed of five systems: (1)
Wideband Code Division Multiple Access (W-CDMA) including TDD and FDD
modes, (2) CDMA 2000 1X, (3) Time Division – Synchronous Code Division
Multiple Access (TD-SCDMA), (4) EDGE (also called UWC-136) and (5) Digital
Enhanced Cordless Telecommunications (DECT).
At the end of the selection phase for IMT-2000, two main families of systems
have emerged, leading to the creation of two groups of standardization (including
operators and manufacturers), namely: (1) 3rd Generation Partnership Project (3GPP),
which developed the W-CDMA standard also called Universal Mobile
Telecommunication System (UMTS) in FDD and TDD modes, and (2) 3GPP2, which
developed the CDMA 2000 standards as an evolution of the IS-95 standards.
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The new high speed technology is part of the 3G UMTS evolution. It provides
additional facilities that are added on to t e basic 3GPP UMTS standard. The upgrades
and additional facilities were introduced at successive releases of the 3GPP standard.
Release 4: This release of the 3GPP standard provided for the
efficient use of IP, a facility that was required because the original
Release 99 focused on circuit switched technology. Accordingly this
was a key enabler for 3G HSDPA.
Release 5: This release included the core of HSDPA itself. It provided
for downlink packet support, reduced delays, a raw data rate (i.e.
including payload, protocols, error correction, etc) of 14 Mbps and
gave an overall increase of around three over the 3GPP UMTS Release
99 standard.
Release 6: This included the core of HSUPA with an enhanced uplink
with improved packet data support. This provided reduced delays, an
uplink raw data rate of 5.74 Mbps and it gave an increase capacity of
around twice that offered by the original Release 99 UMTS standard.
Also included within this release was the MBMS, Multimedia
Broadcast Multicast Services providing improved broadcast services,
i.e. Mobile TV.
Release 7: This release of the 3GPP standard included downlink
MIMO operation as well as support for higher order modulation up to
64 QAM in the uplink and 16 QAM in the downlink. However it only
allows for either MIMO or the higher order modulation. It also
introduced protocol enhancements to allow the support for Continuous
Packet Connectivity (CPC).
Release 8: This release of the standard defines dual carrier operation
as well as allowing simultaneous operation of the high order
modulation schemes and MIMO. Further to this, latency is improved to
keep it in line with the requirements for many new applications being
used.
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HSDPA PRINCIPLE
HSDPA is based on a combination of technologies. Significant is the
introduction of a new transmission channel for the user data, the High Speed
(Physical) Downlink Shared Channel, HS-(P) DSCH. Multiple users share the air
interface resources available on this channel. An intelligent algorithm in the Node B
decides which subscriber will receive a data packet at which time. This decision is
reported to the subscribers via a parallel signaling channel, the High Speed Shared
Control Channel, HSSCCH. In contrast to UMTS, where a new data packet can be
transmitted at least every 10 ms, with HSDPA data packet transmission can occur
every 2 ms.
Another important innovation is the use of an adaptive modulation and coding
procedure. Every subscriber regularly sends messages regarding the channel quality to
the Node B. Depending on the quality of the mobile radio channel, the Node B selects
a suitable modulation and coding for the data packet that offers satisfactory protection
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against transmission errors and that optimizes the use of resources on the air interface.
The Node B can select from the modulation methods QPSK (quadrature phase shift
keying) and 16QAM (quadrature amplitude modulation). While QPSK is already
being used in UMTS release 99, 16QAM provides high data rates specifically for
HSDPA.
In order to achieve robust data transmission, HSDPA uses a HARQ (Hybrid
Automatic Repeat Request) protocol. If a UE receives a data packet with errors, it
requests the data packet again. When repeating the packet transmission, the Node B
can select a different coding version that provides the subscriber with better reception
of the packet (incremental redundancy). This coding version is often referred to as
“redundancy and constellation version” or in short “redundancy version” (RV
version). When a packet has been transmitted to the UE, the Node B has to wait until
an acknowledgement (ACK) or negative acknowledgement (NACK) is received for
this particular packet (so-called stop-and-wait transmission mechanism).. One UE has
to support up to 8 parallel HARQ processes which are equivalent to up to 8
independent HARQ stop-and-wait transmission mechanisms. User feedback about
channel quality as well as packet acknowledgements or negative acknowledgements is
provided in the uplink on the High Speed Dedicated Physical Control Channel, HS-
DPCCH.
KEY HSDPA TECHNOLOGY ENHANCEMENTSHSDPA was designed to increase downlink packet data throughput of UMTS
by means of:
1. Shared channel transmission
2. Adaptive Modulation and Coding (AMC)
3. Fast Hybrid Automatic Repeat Request (H-ARQ)
4. Fair and fast scheduling at Node B
5. Fast cell site selection (FCSS)
6. Short transmission time interval (TTI)
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1. SHARED CHANNEL TRANSMISSION
Several new channels are introduced in release 5. A new transport
channel named High-Speed Downlink Shared Channel (HS-DSCH) is the primary
radio bearer. For the associated signaling a channel called high-speed shared control
channel (HS-SCCH) has been added in the downlink and in the uplink the high-speed
dedicated
HS-(P) DSCH Structure
The transport channel HS-DSCH is mapped on one or more physical channels
of type HS-PDSCH. The HS-PDSCH is always spread with spreading factor 16. One
HS-DSCH transport block is transmitted in a transmission time interval (TTI) of 2 ms
(corresponding to 3 timeslots). If UE category allows, HS-DSCH transport blocks can
be scheduled to the UE continuously, i.e. in every TTI. Less complex UEs
corresponding to a lower UE category can only process data received in every second
or even every third TTI. This is described by the so-called inter TTI distance
parameter. An inter TTI distance of 1 equals continuous HS-PDSCH transmission (in
case data is available for transmission). QPSK or 16QAM are available as modulation
scheme on the HS-PDSCH. Figure outlines the structure of the HS-(P) DSCH.
STRUCTURE OF HS-(P) DSCH
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HS-SCCH Structure
The HS-SCCH is a fixed rate downlink physical channel, spread with
spreading factor 128. One UE has to monitor up to 4 HS-SCCH channels. The UE is
informed by higher layers at call setup which HS-SCCH channels to monitor. The
HS-SCCH contains scheduling and control information (UE identification, HS-
PDSCH channelization codes, HSPDSCH modulation scheme information, transport
block size information, HARQ process information, redundancy and constellation
version, new data indicator). Figure outlines the HS-SCCH structure:
STRUCTURE OF HS-SCCH
The HS-PDSCH starts 2 timeslots after the start of the corresponding HSSCCH.
HS-DPCCH Structure
The HS-DPCCH is an uplink physical channel used to carry control
information: HARQ ACK/NACK and Channel Quality Information. Figure outlines
the structure of the HS-DPCCH.
STRUCTURE OF HS-DPCCH
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The Channel Quality Information consists of a CQI value. There are different
CQI tables specified for different UE categories, reflecting the level of UE
implementation complexity. The CQI values regularly reported by the UE are
interpreted by the Node B as proposal how to format the HS-(P) DSCH. With this
format, the resulting block error rate of the HS-DSCH is predicted by the UE to be
below 0.1. The higher the CQI value, the more demanding the HS-DSCH
transmission format, i.e. the better the radio link quality has to be.
2. ADAPTIVE MODULATION AND CODING (AMC)
HSDPA uses both the modulation used in WCDMA, namely
Quadrature Phase Shift Keying (QPSK) and under good radio conditions, an advanced
modulation scheme, 16 Quadrature Amplitude Modulation (16 QAM). The benefit of
16 QAM is that four bits of data are transmitted in each radio symbol as opposed to
two with QPSK. 16 QAM increases data throughput, while QPSK is available under
adverse conditions.
Depending on the condition of the radio channel, different levels of forward
error correction (channel coding) can also be employed. For example, a three quarter
coding rate means that three quarters of the bits transmitted are user bits and one
quarter is error correcting bits. The process of selecting and quickly updating the
optimum modulation and coding rate is referred to as fast link adaptation.
QUADRATURE PHASE SHIFT KEYING (QPSK)
Sometimes known as quaternary or quadriphase PSK, 4-PSK, QPSK uses four
points on the constellation diagram, equispaced around a circle. With four phases,
QPSK can encode two bits per symbol, shown in the diagram with Gray coding to
minimize the BER — twice the rate of BPSK. Analysis shows that this may be used
either to double the data rate compared to a BPSK system while maintaining the
bandwidth of the signal or to maintain the data-rate of BPSK but halve the bandwidth
needed. Although QPSK can be viewed as a quaternary modulation, it is easier to see
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it as two independently modulated quadrature carriers. With this interpretation, the
even (or odd) bits are used to modulate the in-phase component of the carrier, while
the odd (or even) bits are used to modulate the quadrature-phase component of the
carrier. BPSK is used on both carriers and they can be independently demodulated.
The modulated signal is shown below for a short segment of a random binary data-
stream.
TIMING DIAGRAM OF QPSK
CONSTELLATION DIAGRAM OF QPSK
16- QUADRATURE AMPLITUDE MODULATION (16- QAM)
Data is spit into two channels, I and Q. As with QPSK, each channel can take
on two phases. However, 16-QAM also accommodates two intermediate amplitude
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SYMBOL
TRANSMITTED
CARRIER PHASE
00 225°
01 135°
10 315°
11 45°
HSDPA
values. Two bits are routed to each channel simultaneously. The two bits to each
channel are added, and then applied to the respective channel’s modulator.
CONSTELLATION DIAGRAM OF 16-QAM
Table below shows
the different throughput rates
achieved based on the
modulation, the coding rate,
and the number of HS-DSCH codes in use. Both Convolutional Coding and Turbo
coding are supported but previously only CC has been supported. Note that the peak
rate of 14.4 Mbps occurs with a coding rate of 4/4, 16 QAM and all 15 codes in use.
MODULATION CODING
RATE
THROUGH
PUT WITH 5
CODES
THROUGH
PUT WITH 10
CODES
THROUGH
PUT WITH 15
CODES
QPSK1/4 600kbps 1.2Mbps 1.8 Mbps2/4 1.2Mbps 2.4 Mbps 3.6 Mbps3/4 1.8Mbps 3.6 Mbps 5.4 Mbps
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SYMBOL
TRANSMITTED
CARRIER
PHASE
CARRIER
AMPLITUDE0000 225° 0.330001 255° 0.750010 195° 0.75
0011 225° 1.00100 135° 0.330101 105° 0.750110 165° 0.75
0111 135° 1.01000 315° 0.331001 285° 0.751010 345° 0.75
1011 315° 1.01100 45° 0.331101 75° 0.75
1110 15° 0.751111 45° 1.0
HSDPA
16 QAM2/4 2.4Mbps 4.8 Mbps 7.2 Mbps3/4 3.6Mbps 7.2 Mbps 10.7 Mbps4/4 4.8Mbps 9.6 Mbps 14.4 Mbps
3. FAIR AND FAST SCHEDULING AT NODE B
It allows the HS-DSCH channel to take advantage of favorable channel
conditions to make best use of available radio conditions. Each UE periodically
reports on the signal quality to Node B (Base Stations). That information is then used
to decide which users will be sent data on the next 2ms frame and how much data can
be sent to each user.
A first approach for fair scheduling can be Round-Robin method where every
user is served in a sequential manner so all the users get the same average allocation
time. However, the requirement of high scheduling rate along with the large AMC
availability with the HSDPA concept, where the channel is allocated according to the
instantaneous
channel conditions. Another popular packet scheduling is proportional fair packet
scheduling. Here, the order of service is determined by the highest instantaneous
relative channel quality. Since the selection is based on relative conditions, still every
user gets approximately the same amount of allocation time depending on its channel
condition.
4. FAST HYBRID AUTOMATIC REPEAT REQUEST (H-ARQ)
Some data will inevitably be corrupted in transit to the device and will have to
be retransmitted. With HSDPA, data retransmission may be handled “locally” by the
base-station improving response times compared to earlier UMTS networks (where
only the more distant RNC could manage data retransmissions). HSDPA employs a
“stop and wait hybrid automatic repeat request” (SAW HARQ) retransmission
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protocol between the base-station and the user device. With HARQ, each device
checks the integrity of its received data in each relevant HS-DSCH TTI. If the data is
correct, the device returns an “ACK” (acknowledging receipt of correct data) signal,
in which case the base-station can move on to the next set of data. If the data is not
successfully received, the device transmits an “NACK” (negative acknowledgement)
and the base-station retransmits the corresponding data. With “soft combining” at the
user device, the earlier set(s) of corrupted data can be combined with subsequently
retransmitted data to increase the likelihood of correctly decoding valid data.
The AMC uses an appropriate modulation and coding scheme according to the
channel conditions. Even after AMC, we may land up with errors in the received
packets due to the fact that the channel may vary during the packet is on the fly. An
automatic repeat request (ARQ) scheme can be used to recover from these link
adaptation errors. When the transmitted packet is received erroneous then the receiver
requests the transmitter for the retransmission of that erroneous packet. The basic
technique is to use the energy of the previously transmitted signal along with the new
retransmitted signal to decode the block. There are two main schemes for H-ARQ,
Chase combining and Incremental redundancy.
Chase Combining involves the retransmission of the same data packet which
was received with errors. Once the retransmission is received, the receiver combines
the soft values of the original signal and the retransmitted signal weighted by the SNR
prior to decode the data packet. It is advantageous as each transmission and
retransmission can be decoded individually (self-decodable), time diversity gain, may
be path diversity gain. The main disadvantage is transmission of the entire packet
again, which is wastage of bandwidth.
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CHASE COMBINING SCHEME
Incremental Redundancy is used to get maximum performance out of the
available bandwidth. Here the retransmitted block consists of only the correction data
to the original data that carries no actual information (Redundancy). The additional
redundant information is sent incrementally when the first, second retransmissions are
received with errors. It is advantageous as it reduces the effective data throughput/
bandwidth of a user and using this for another user. The main disadvantages are the
systematic bits are only sent in the first transmission and not with the retransmission
which makes the retransmissions non-self decodable. So, if the first transmission is
lost due to large fading effects there is no chance of recovering from this situation.
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INCREMENTAL REDUNDANCY
Although the HSDPA standard supports both chase combining and
incremental redundancy, it has been shown that incremental redundancy performs
almost always better than chase combining, at the cost of increased complexity,
though.
5. FAST CELL SITE SELECTION (FCSS)
HSDPA does not use soft handover. This is because the AMC, H-ARQ and
fast packet scheduling are techniques that require a constant one-to-one connection
between the HSDPA mobile terminal and the BS. Thus hard handover, in which the
destination BS is selected each time the cell changes, is needed. Since the only traffic
supported by HSDPA is delay-tolerant data traffic soft handover is also not as
necessary as when dealing with voice traffic.
6. SHORTER TRANSMISSION TIMEThe shorter time interval enables higher speed transmission in the physical
layer, so that the system will be more reactive to changing link conditions and can
reallocate capacity to users quicker.
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HSDPA ARCHITECTURE
The protocol structure for HSDPA is outlined in figure. Compared to UMTS
release 99, significant functionality has been moved to the Node B in release 5. Thus,
new MAC-hs (Medium Access Control– high speed) protocol entity has been
introduced in the Node B. It is responsible for flow control, scheduling and priority
handling of data, control of HARQ processes and selection of appropriate transport
formats and resources. The MAC-hs entity is terminated on the UE side.
HSDPA PROTOCOL ARCHITECTURE
Within the Radio Resource Control (RRC) protocol, existing messages for
bearer setup, reconfiguration and release were modified to support HSDSCH. New
information elements were introduced, e.g. to inform the UE about the HS-SCCH set
to monitor and about the measurement cycle for the CQI reporting.
Mobility for HSDPA is based on existing release 99 handover procedures. For
the HS-PDSCH no macro diversity is applied, i.e. a specific HSPDSCH is transmitted
in a single cell only.
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PERFORMANCE OF HSDPA
The performance of each technology is determined by a number of constraints,
including the throughput, the latency etc.
The throughput is the data rate of the standard. The theoretical maximum
throughput is the throughput rate available to a single connection under ideal
circumstances. These speeds may not be achieved regularly in typical usage. The
typical throughput is what users have experienced most of the time when well-within
the usable range to the base station. This value is not known for the newest
experimental standards. Note that these figures cannot be used to predict the
performance of any given standard in any given environment, but rather as
benchmarks against which actual experience might be compared.
The latency is the time taken for the smallest packet to travel between the user
terminal and base station. Just as important as throughput is network latency, defined
as the round-trip time it takes data to traverse the network. Each successive data
technology from GPRS forward reduces latency, with HSDPA networks having
latency as low as 70 milliseconds. HSUPA brings latency down even further, as will
3GPP LTE. Ongoing improvements in each technology mean all these values will go
down as vendors and operators fine tune their systems. Figure shows the latency of
different 3GPP technologies.
LATENCY OF DIFFERENT TECHNOLOGIES
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Spectral efficiency, spectrum efficiency or bandwidth efficiency refers to the
information rate that can be transmitted over a given bandwidth in a specific
communication system. It is a measure of how efficiently a limited frequency
spectrum is utilized by the physical layer protocol, and sometimes by the media
access control (the channel access protocol).
NET BIT RATE PER
FREQUENCY
CHANNEL (Mbps)
BANDWIDTH PER
FREQUENCY
CHANNEL (MHz)
SPECTRAL
EFFICIENCY
(bps/Hz/site)GSM 0.013 0.2 0.17EDGE 0.384 0.2 0.33WCDMA 0.384 5 0.51HSDPA 14.4 5 2.88LTE 326.4 20 16.32
COMPARISON WITH WCDMA (R’99)
3GPP’s Release 99 specified the first UMTS 3G network. The technology
used in R’99 systems is called W-CDMA. HSDPA is a high speed data enhancement
to WCDMA systems like EDGE was for GSM/GPRS and will most often be deployed
with an R’99 system. That is WCDMA is used for voice and HSDPA for data on the
same network, they will thus have to share bandwidth and power. HSDPA is evolved
from and backward compatible with Release 99 WCDMA systems.
WCDMA (R’99) HSDPAModulation Scheme QPSK QPSK, 16- QAMDownlink Multiple
Access
CDMA CDMA- TDMA
Uplink Multiple Access CDMA CDMADuplex Method FDD FDDChannel Bandwidth 5 MHz 5MHzFrame Size 10 ms 2 msCoding CC CC, TurboDownlink Peak Data
Rate
384 Kbps 14.4 Mbps
COMPARISON WITH COMPETING TECHNOLOGIES
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Competing wireless technologies with HSDPA are Mobile WiMAX (IEE
802.16e) and 1X EvDo in CDMA 2000.
COMPARISON WITH MOBILE WIMAX AND EV- DO
HSDPA and Mobile WiMAX are high speed mobile technologies with
different backgrounds. HSDPA is a data enhancement for a voice-centric 3GPP
system while WiMAX is data-centric broadband technology that has an added feature
of mobility. Many operators around the world have invested in R’99 UMTS networks.
For them
HSDPA offers a significant service upgrade and an opportunity to accelerate the
Return of Investment. HSDPA networks are already widely deployed and handsets
have been on the market since 2006. For Mobile WiMAX it is necessary to build new
networks, and the manufacturing of handsets has been quite complicated and required
a totally new set of chips and platforms. EvDo is standardized by 3rd Generation
Partnership Project 2 (3GPP2) as part of the CDMA2000 family of standards and has
been adopted by many mobile phone service providers around the world – particularly
those previously employing CDMA networks. It is also used on the Globalstar
satellite phone network
Despite their different background there are several technical features that the
three technologies have in common. Those include Adaptive Modulation and Coding
(AMC), Hybrid ARQ and Fast Scheduling.
In OFDMA systems users are allocated different portions of the channel where
as in CDMA each user transmits over the entire channel. This means that in OFDMA
there is no multiple access interference (MAI) between multiple users. In CDMA
orthogonal spreading codes are used to avoid MAI but due to the uplink
synchronization issues, asynchronous CDMA is used in the uplink in most practical
CDMA systems and there will be interference and reduced spectral efficiency. As
only a portion of the channel is occupied by the WiMAX signals frequency selective
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scheduling can be used to choose sub channels with the best condition at each time
and hence improve QoS. For smart antenna technologies the processing complexity
scales with the channel bandwidth. Since in CDMA the signals occupy the entire
bandwidth this becomes quite a problem when used in broadband wireless channels
and limits the options of using advanced Antenna Technology. OFDMA on the other
hand is well suited for these technologies. Mobile WiMAX will most commonly use
TDD while HSDPA generally uses FDD. FDD is more efficient than TDD in the case
of symmetric traffic but TDD allow for asymmetric traffic and as the downlink traffic
is usually much heavier than the uplink traffic, asymmetric traffic can be very
practical. TDD requires system-wide frame synchronization to counter interference
issues and the discontinuous transmissions reduce the average power. On the
other hand TDD assures channel reciprocity and thus better supports link adaptation,
MIMO and other advanced antenna technologies.
The 60% longer radius of HSDPA gave it an advantage in economic feasibility
while 70% higher throughput for Mobile WiMAX did not give any economic
advantage. The performance of HSPA and Mobile WiMAX technologies is
comparable: Mobile WiMAX does not offer any technology advantage over HSPA.
Both technologies offer similar peak data rates, spectral efficiency and network
complexity. However, Mobile WiMAX requires more sites to offer the same coverage
and capacity as HPSA.
EvDo is standardized by 3rd Generation Partnership Project 2 (3GPP2) as part
of the CDMA2000 family of standards and has been adopted by many mobile phone
service providers around the world – particularly those previously employing CDMA
networks. It is also used on the Globalstar satellite phone network. EV-DO uses many
of the same techniques for optimizing spectral efficiency as HSPA, including higher
order modulation, efficient scheduling, turbo-coding, and adaptive modulation and
coding. For these reasons, it achieves spectral efficiency that is virtually the same as
HSPA. The 1x technologies operate in the 1.25 MHz radio channels, compared to the
5 MHz channels UMTS uses. This result in lower theoretical peak rates, but average
throughputs for high level of network loading is similar. Under low to medium-load
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conditions, because of the lower peak achievable data rates, EV-DO or EVDO Rev A
achieves a lower typical performance level than HSPA. Operators have quoted 400 to
700 kilobits per second (kbps) typical downlink throughput for EV-DO Rev 035 and
between 600 kbps and 1.4 Mbps for EV-DO Rev A.36.
One challenge for EV-DO operators is that they cannot dynamically allocate
their entire spectral resources between voice and high-speed data functions. The EV-
DO channel is not available for circuit-switched voice, and the 1xRTT channels offer
only medium speed data. In the current stage of the market, where data only
constitutes a small percentage of total network traffic, this is not a key issue. But as
data usage expands, this limitation will cause suboptimal use of radio resources.
Another limitation of using a separate channel for EV-DO data services is that it
currently prevents users from engaging in simultaneous voice and high-speed data
services, whereas this is possible with UMTS and HSPA. Many users enjoy having a
tethered data connection from their laptop—by using Bluetooth, for example—and
being able to initiate and receive phone calls while maintaining their data sessions.
HSDPA Mobile WiMAX EV-DOBase Standard WCDMA IEEE 802.16e CDMA 2000
Duplex Method FDD TDD FDD
Downlink Multiple
Access
CDMA-TDMA OFDMA TDM
Uplink Multiple Access CDMA OFDMA CDMA
Frequency 900MHz/1.8/2.1GHz 2.3/2.5/3.5GHz 450/850/900Mhz/1.8G
HzChannel Bandwidth 5MHz Scalable: 5, 7,8.75,
10MHz
1.25MHz
Frame Size DL= 2ms, UL =10ms 5ms DL=1.67ms, UL=6.67ms
Modulation Downlink QPSK, 16-QAM QPSK, 16-QAM,64-
QAM
QPSK, 8-PSK, 16-QAM
Modulation Uplink BPSK, QPSK QPSK, 16-QAM BPSK,QPSK, 8-PSK
Coding CC, Turbo CC, Turbo CC, Turbo
Downlink Peak Data
Rate
14.4Mbps 46Mbps 2.45Mbps
Uplink Peak Data Rate 2.3Mbps 46Mbps 0.15Mbps
Scheduling Fast scheduling in DL Fast scheduling in DL,
UL
Fast scheduling in DL
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HSDPA
H-ARQ Chase Combining Chase Combining Incremental
RedundancyHandoff Network Initiated Hard
Handoff
Network Optimized
Hard Handoff
Virtual Soft
HandoffCoverage 3 Miles <2 Miles >3 Miles
Mobility High Low/ Mid High
CURRENT DEPLOYMENT OF HSDPA
HSDPA (High Speed Downlink Packet Access) is an upgrade to
UMTS/WCDMA. HSDPA increases the download speeds by up to 3.5 times, initially
delivering typical user data rates of 550 to 800 kbps. Improvements to the downlink,
through HSDPA, were the first upgrade steps available to operators seeking to deploy
mobile broadband services as a part of 3GPP Release 5. HSDPA speeds are ideal for
bandwidth-intensive applications, such as large file transfers, streaming multimedia
and fast Web browsing. HSDPA also offers latency as low as 70 to 100 milliseconds
(ms) making it ideal for real-time applications such as interactive gaming and delay-
sensitive business applications such as Virtual Private Networks.
High Speed Downlink Packet Access is predominately a software upgrade to
Release 99 of the UMTS standard. HSDPA has been commercially available since
December 2005, when Cingular Wireless – now AT&T – launched the world's first
large scale HSDPA service. There are more than 300 HSDPA networks commercially
deployed or in various stages of deployment in more than 115 countries (May 2009).
International roaming is available as the technology falls back on UMTS, EDGE and
GPRS for the continuation of voice and data services. Sony Ericsson Z-50, K850i,
W910iare some HSDPA supported handsets available in markets. In November 2003,
Motorola became the first vendor to demonstrate HSDPA on a commercially
available UMTS base station at its Swindon, UK facility. HSDPA supported Motorola
handsets are RAZRZ8 and RAZRV9. Nokia N95, E51, E90, 6120Clasic are some
HSDPA supported handsets from Nokia which can provide a maximum downlink
speed of 3.6Mbps.HSDPA devices also include 39 wireless routers, 61 laptops and
100 devices for laptop connectivity (USB modems etc). The number of HSDPA
networks, devices and subscribers is constantly growing. For example
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HSDPA
WCDMA/HSDPA was responsible for 75% of the mobile subscription growth in
Western Europe in 2007. In India MTNL DOLPHIN has started 3G Services under
the brand name of 3G Jadoo where Jadoo means Magic in Hindi. While BSNL has
launched 3G HSDPA services with speed up to 2 Mbit/s at 12 Indian Cities on
27.02.2009. The BSNL’s Commercial 3G service are available now in Amabala,
Agara, Dehardun, Jammu, Jaipur, Jalandhar, Lacknow, Shimla, Patna, Ranchi, Haldia
and Durgapur. They are collaborating with Nokia, Sony and Samsung for offering 3G
capable mobile handsets along with packages in the market.
HSDPA usually requires only new software and base station channel cards,
instead of necessitating the replacement of major pieces of infrastructure from UMTS
and does not require additional spectrum for deployment. As a result, UMTS
operators can deploy HSDPA quickly and cost-effectively. In fact, most operators that
deploy 3G UMTS are deploying an HSDPA-ready network.
HSDPA technology significantly improves the UMTS downlink performance
through techniques, such as adaptive modulation and coding, hybrid ARQ (HARQ)
and fast scheduling. On the receiving side, initial HSDPA User Equipment (UE)
solutions were based on single antenna CDMA rake receiver structures, similar to
Release 99 UMTS receiver structures. The corresponding minimum performance
requirement for HSDPA rake receivers was specified in Release 5. While the single
antenna rake receivers worked very well for conventional UMTS and met initial
system needs for HSDPA, advanced receiving technologies were later used to achieve
even higher HSDPA throughputs. To achieve this goal, 3GPP studied two applicable
techniques (receive diversity and advanced receiver architectures) as well as their
minimum performance improvement and has specified them in Release 6.
HSDPA also benefits operators by making more efficient use of spectrum, up
to three times more capacity than UMTS. This efficiency means that operators can
easily and cost-effectively accommodate more users and services without having to
buy additional spectrum just to keep up with growth. That efficiency also reduces
operators' overhead costs, and thus, makes them better able to price their services at a
point that is competitive yet profitable.
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HSDPA
HSDPA is backward-compatible with UMTS, EDGE and GPRS. This design
benefits customers when they travel to areas that have not yet been upgraded to
HSDPA, as their HSDPA-enabled handsets and modems will still provide fast packet-
data connections. This design also benefits operators and application developers
because applications designed for UMTS also run on HSDPA networks and devices.
HSDPA benefits from the scope and scale of the GSM ecosystem of vendors.
Vendors currently offer more than 1,300 models of HSPA/HSDPA devices at a
variety of price points. Besides handsets and PC card modems, HSPA/HSDPA is also
embedded in many laptops from major vendors such as Acer, Dell, Fujitsu Siemens,
HP, Lenovo and Panasonic. Embedded modems are particularly attractive to
enterprises because CIOs and IT managers do not have to worry about whether a
particular modem is compatible with a particular laptop model. Devices also are
available at most GSM frequencies, enabling global roaming.
DEPLOYMENT CHALLENGES: INDIAN FACTS
Since there is no copper laid out in rural India, DSL is not an option to deliver
high bandwidth services. Given the existing and potential coverage realized by GSM/
GPRS cellular systems, the incremental cost of implementing HSDPA should be
much lower than that of setting up any other Greenfield wireless network. WiMAX
could be a challenger, but its maturity is currently much lower than HSDPA.
India has seen a rapid increase in wireless coverage. GSM and CDMA are the
competing technologies. As of July 2009, the wireless penetration at 59.83 million is
significantly higher than landline penetration, which is at 47.17 million. The monthly
cellular additions are getting closer to 3 million/month, with GSM technology base
having a higher subscriber base accounting for about 80%. GSM coverage enables
quick and easy HSDPA access. As can be seen, the range of HSDPA is severely
limited to around 2Km cells, as compared the current GSM/GPRS systems that have
range that is one order of magnitude higher. This could mean that the current
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HSDPA
GSM/GPRS infrastructure is largely insufficient for HSDPA coverage, and significant
additional capex may be required to deploy HSDPA into rural areas. The entire cost
benefit gains of HSDPA due to its higher capacity could thus be offset due to the cost
increase due to lower range.
Increasing the range of HSDPA is a key research problem that determines its
success for rural India. Lower frequencies reach further. Lower rate transmissions can
span a higher range.
RELEASES BEYOND HSDPA
Work is now staring on developing the standards for High Speed Uplink
Packet Access (HSUPA) to improve the data rates on the 3G W-CDMA mobile or cell
phone standard. With the cellular telecommunications standards established and work
progressing to introduce the equipment for High Speed Downlink Packet Access
(HSDPA), the standards are now starting to be developed to enable the uplink from
the mobile handset or User Equipment (UE) to the base station (Node B) to be able to
handle data at similar speeds. This is known as HSUPA and it will enable new
features including full video conferencing to be introduced. 3G HSPA of High Speed
packet Access is the combination of two technologies. 3G HSPA is widely deployed
and providing significantly increased data transfer rates required for the variety of
data applications including mobile broadband for Internet connectivity now being
used by mobile users. As 3G UMTS HSPA is normally a relatively straightforward
upgrade based around a software change, its incorporation involves a relatively low
cost upgrade. As the use of 3G HSPA is able to increase the efficiency of the overall
network, reducing the cost per bit, then it is often a very cost effective upgrade.
Evolved HSPA provides HSPA data rates up to 42 Mbit/s on the downlink and
22 Mbit/s on the uplink with MIMO technologies and higher order modulation.
MIMO on CDMA based systems acts like virtual sectors to give extra capacity closer
to the mast. The 42Mbit/s and 22Mbit/s represent theoretical peak sector speeds. The
actual peak speed for a user closer to the mast may be about 14Mbit/s. As of August
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HSDPA
2009, there are 10 HSPA+ networks running in the world at 21Mbit/s and the first
28Mbit/s network has been completed in Italy. The first to launch was Telstra in
Australia in late 2008, with Australia-wide access in February 2009 with speeds up to
21Mbit/sec.
LTE (Long Term Evolution) is the last step toward the 4th generation of radio
technologies designed to increase the capacity and speed of mobile telephone
networks. Where the current generation of mobile telecommunication networks are
collectively known as 3G (for "third generation"), LTE is marketed as and called 4G
insinuating that it's the "fourth generation". The LTE specification provides downlink
peak rates of at least 100 Mbps, an uplink of at least 50 Mbit/s and RAN round-trip
times of less than 10ms. LTE supports scalable carrier bandwidths, from 20 MHz
down to 1.4 MHz and supports both Frequency Division Duplexing and Time
Division Duplexing.
CONCLUSION
The HSDPA concept facilitates peak data rates exceeding 2 Mbps and
theoretically reaching 10 Mbps. The cell throughput gain over previous releases has
been evaluated to be in the order of 50-100% or more, which is highly dependent on
factors such as the radio environment and the service provision strategy of the
network operator. Practical HSDPA user bit rates even in large macro cells can be
similar to broadband home DSL lines. As HSDPA enables more bits to be transferred
with the same radio frequency, it also enables lower cost per bit than Release'99 based
WCDMA. The H-ARQ technique which is best suited in HSDPA would be partial
incremental redundancy. Performance of partial IR is in between chase combining and
IR. Further evolution of HSDPA peak data rates can be achieved with multiple-input
multiple-output (MIMO) antenna techniques of 3GPP Rel.'6. No changes are required
to the networks except increased capacity within the infrastructure to support the
higher bandwidth.
REFERENCES
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HSDPA
1. 3rd Generation Partnership Project (3GPP). Available at:
http://www.3gpp.org/
2. 3rd Generation Partnership Project 2 (3GPP2). Available at:
http://www.3gpp2.org/
3. Global Mobile Suppliers Association (GSA). Available at:
http://www.gsacom.com
4. WiMAX Forum, http://www.wimaxforum.org/
5. P. Rysavy, 3G Americas. Mobile Broadband: EDGE, HSPA and LTE.
Available at: www.3gamericas.org/English/Technology_Center/WhitePapers/
6. Comparison of Mobile WiMAX and HSDPA: Kolbrun Johanna Runarsdottir
7. Wikipedia contributors, "UMTS frequency bands,"
http://en.wikipedia.org/w/index.php?
title=UMTS_frequency_bands&oldid=186921008
8. High-Speed Downlink Packet Access - Wikipedia, the free encyclopedia
http://en.wikipedia.org/w/HSDPA/
GLOSSARY OF TERMS
1xEV-DO One Carrier Evolved, Data Optimized
1xEV-DV One Carrier Evolved, Data Voice
2G Second Generation
3G Third Generation
3GPP 3G Partnership Project
3GPP2 3G Partnership Project 2
4G Fourth Generation
ACK Acknowledgement
ADSL Asynchronous Digital Subscriber Line
AMC Adaptive Modulation and Coding
ARQ Automatic Repeat Request
BTS Base Station
CDMA Code Division Multiple Access
DPCH Dedicated Physical Channel
BM II COLLEGE OF ENGINEERING 27 DEPT. OF ECE
HSDPA
DL Downlink
EDGE Enhanced Data Rates for GSM Evolution
E-UTRAN Enhanced UMTS Terrestrial Radio Access Network
FDD Frequency Division Multiplex
FP Frame Protocol
GPRS General Packet Radio Service
GSM Global System for Mobile communication
GSMA GSM Association
HLR Home Location Register
HO Handover, Handoff
HSDPA High Speed Downlink Packet Access
HSPA High Speed Packet Access
HSUPA High Speed Uplink Packet Access
H-ARQ Hybrid- ARQ
ITU International Telecommunication Union
IEEE Institute of Electrical and Electronic Engineers
LAN Local Area Network
LTE Long Term Evolution
MAC Media Access Control
MAC-hs Medium Access Control – high speed
MIMO Multiple Input Multiple Output
MMS Multimedia Message Service
MS Mobile Station
MSC Mobile Switching Centre
NACK Negative Acknowledgement
OFDMA Orthogonal Frequency Division Multiple Access
PER Packet Error Rate
PHY Physical layer
PSTN Public Switched Telephone Network
QAM Quadrature Amplitude Modulation
QoS Quality of Service
QPSK Quadrature Phase Key Shifting
RAN Radio Access Network
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HSDPA
RF Radio Frequency
RL Reverse Link (also Radio Link)
RNC Radio Network Controller
SGSN Serving GPRS Support Node
SIM Subscriber Identification Module
SIMO Single Input Multiple Output
SMS Short Message Service
SNR Signal-to-Noise Ratio
TDD Time Division Duplex
TDMA Time Division Multiple Access
TTI Transmission Time Interval
UE User Equipment
UL Uplink
UMTS Universal Mobile Telephony System
UTRAN UMTS Terrestrial Radio Access Network
VoIP Voice over IP
VPN Virtual Private Network
WCDMA Wideband CDMA
WiFi Wireless Fidelity
WAP Wireless Application Protocol
WiBro Wireless Broadband
WiMAX Worldwide Interoperability for Microwave Access
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