Delivering Voice Using HSPA

TABLE OF CONTENTS
EXECUTIVE SUMMARY .............................................................................................................................. 2
I.
THE GROWTH OF HSPA ...................................................................................................................... 3
II. EVOLUTION OF VOICE SERVICE OVER 3GPP MOBILE NETWORKS .............................................. 5
A. GSM CS VOICE .................................................................................................................................. 5
B. UMTS CS Voice ................................................................................................................................... 5
C. Voice over HSPA ................................................................................................................................. 6
D. Voice over LTE .................................................................................................................................... 8
III. BENEFITS OF VOICE OVER HSPA ...................................................................................................... 9
IV. VoHSPA TECHNICAL OPTIONS ......................................................................................................... 11
A. IR.58 Minimum Mandatory Feature Set ............................................................................................. 11
1. Non-Radio features ......................................................................................................................... 11
2. Radio (and related Packet Core) features ..................................................................................... 11
B. Additional features ............................................................................................................................. 14
V. STATUS OF VoHSPA REALIZATION.................................................................................................. 17
VI. CONCLUSION ...................................................................................................................................... 19
REFERENCES ............................................................................................................................................ 21
ABBREVIATIONS ....................................................................................................................................... 23
ACKNOWLEDGEMENTS ........................................................................................................................... 25
Page 1
EXECUTIVE SUMMARY
Over the next few years HSPA will be, based simply on sheer projected number of devices, the
overwhelming technology for delivering mobile broadband technology to consumers. The consensus is
that this will continue to be the case through the remainder of the decade, even as Long Term Evolution
(LTE) begins proliferating.
As a result, the mobile industry is continually striving to improve HSPA technology. One important facet
of this effort relates to the delivery of voice services. Up to now, mobile voice services have been
delivered by service providers using traditional circuit-switched (CS) technology. Largely absent have
been the benefits to be derived from leveraging packet-switched (PS) and Internet Protocol (IP) based
technologies by operators. (This is in contrast to third party, over the top voice over IP [VoIP] services.)
The industry is poised, however, to introduce voice services using PS, IP-based technologies. Once
deployed, both mobile network operators and consumers stand to benefit significantly from more
innovative, robust and efficient services.
This paper describes the technological features that are being developed to make Voice over HSPA
(VoHSPA) a reality. It describes the two potential options for VoHSPA. The first option leverages IP
Multimedia Subsystem (IMS) technology developed in conjunction with Long Term Evolution (LTE), and is
referred to as IMS Voice over HSPA or simply IMS Voice. The other option delivers voice by modifying
existing circuit-switch based techniques so that those communications can be transmitted over an HSPA
infrastructure, and is referred to as CS Voice over HSPA (CSoHS).
This paper reports on the status of the ecosystem for commercializing the needed technology features
under both options. As detailed later in the paper, with one exception, all of the features considered
necessary for a robust VoHSPA service are available now or will be available from vendors in 2012-2013
for operator testing and validation.
4G Americas hopes that this paper serves as a catalyst for the development of these technologies,
illuminating both the progress that has been made as well as what remains to be achieved to make
VoHSPA a reality for consumers.
Page 2
I.
THE GROWTH OF HSPA
Globally, as of February 1, there were 423 HSPA networks in 160 countries in operation. And based on
the number of subscriptions, HSPA stands as the predominant means of providing mobile broadband
services globally. Over the next several years, the gap between HSPA and other technologies will widen.
As illustrated below, by 2016 45 percent of all mobile subscriptions will be based on HSPA technology, as
compared to 8 percent for LTE and 7 percent for CDMA.
Figure 1. Global Mobile Technology Forecast 2011-2016 (Source: Informa)
This trend is also evident in the Americas. For example, by the end of 2015 it is forecast that the total
number of HSPA subscriptions will surpass the total number of GSM subscriptions in Latin America. This
is depicted in the graph below.
Figure 2. Latin American Technology Growth Forecast 2011-2016 (Source: Informa)
Page 3
These trends have some important implications. One relates to the evolutionary path for mobile voice
telephony service, which has been one of, if not the most important service provided over mobile
networks, and up to the present, the main source of revenues for mobile operators. For example, will
preparations to deliver voice services over emerging LTE networks be leveraged to improve mobile voice
service over existing mobile networks? And what provisions are being made so that legacy voice services
can coexist and interoperate with newer voice services?
The mobile industry is working to address these questions. In order to better appreciate these
developments, some background is provided in the next section. Note that this information, and more
generally this paper, deals with the evolution of mobile voice telephony services in 3GPP based mobile
networks, that is, carrier grade telephony service provisioned by mobile operators, in contrast to over the
top (OTT) VoIP service provided by third parties over the operator’s network but without the involvement
of the mobile operator itself in the service provision.
Page 4
II.
EVOLUTION OF VOICE SERVICE OVER 3GPP MOBILE NETWORKS
A. GSM CS VOICE
Cellular service based on GSM technology was launched in the early 1990s. Based on digital CS
technology to provide full duplex (simultaneous two way) voice telephony. GSM employs a dedicated
timeslot over the air interface to carry individual voice communications from the Mobile Station (MS) to the
Base Transceiver Station (BTS), transiting on from there toward the core network using dedicated trunk
resources. This method of providing radio resources is referred to as Time Division Multiple Access
(TDMA), and it allows a frequency pair to carry either 8 (full rate) or 16 (half rate) time slots. The following
figure illustrates the basic network elements for carrying GSM CS voice.
Figure 3. Illustration of network elements for providing GSM CS voice
B. UMTS CS VOICE
Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular technology for
networks based on the GSM standard, and was first launched in the early 2000s. UMTS employs
Wideband Code Division Multiple Access (W-CDMA) radio access technology to offer greater spectral
efficiency and bandwidth for both CS voice and PS data to mobile network operators than TDMA radio
access offered with GSM. The core network supporting UMTS CS voice does not differ much from the
one supporting GSM CS voice. This allows the UMTS and GSM radio access network to share a common
core network as shown in the figure below.
Page 5
PSTN
GSM BTS
Abis
Air
BSC
SS7
A
2/3G
MSC/
VLR
(Um)
Iu-cs
NodeB
Air
(Uu)
RNC
Iub
Figure 4. Illustration of network elements for providing both UMTS and GSM CS voice service
C. VOICE OVER HSPA
The traditional mechanism of mapping the CS voice connection over a Dedication Transport Channel
(DCH) in the radio network has been in place since the very first UMTS/W-CDMA standard was
A
established in version 3.0.0 of 3GPP Rel-99.
An HSPA radio service was only later introduced,
specifically targeting high speed packet access, and thus only PS data could initially be mapped onto it.
Subsequently a number of voice related optimizations were introduced to HSPA, enabling Voice over
HSPA (VoHSPA), initially designed to carry digital CS voice traffic over the PS HSPA radio layer
(CSoHS). This promised to be significantly more efficient than the traditional CS voice over DCH service,
both in terms of system capacity and UE power consumption. From a radio perspective there is little
difference whether data bits flow over a CS or PS connection. Thus, in order to be able to benefit from
voice related HSPA improvements, the limitation preventing CS connections from being mapped to the
HSPA radio layer was removed in the Rel-8 specifications. (Notably the feature capability indication bit
for UE support of CSoHS was introduced in the Rel-7 specifications, making it “early implementable,” that
is, a Rel-7 compliant UE is able to support CSoHS even though the feature is technically part of Rel-8
specifications.)
The graphic below depicts CSoHS implementation.
Page 6
Scheduler prioritizes
voice packets
AMR adaptation
possible
CS mapped to R99 or HSPA bearer
depending on terminal capability
Transport
queues etc
CS R99
IuCS
HSPA scheduler
Combined
to one
carrier
AMR
adapt.
HSPA
IuPS
PS R99
NodeB
RNC
Figure 5. Illustration of CSoHS Implementation
In CSoHS, the already digitized voice packets use HSPA channels for transport back to the existing CS
infrastructure immediately beyond the radio access network at the Radio Network Controller (RNC).
Only certain relatively straightforward changes are needed in the network and in the UEs to enable
P
CSoHS, as will be explained further below.
CS voice
over HSPA
Voice over IP
over HSPA
Traditional CS
voice over DCH
Another option for moving voice traffic over these high-speed data channels has emerged more recently.
This approach will carry voice natively using IP (that is, VoIP) in conjunction with IP Multimedia
Subsystem (IMS) technology standardized in Rel-8. The graphic below highlights the distinctions
between traditional Rel-99 CS Voice, CSoHS and IMS Voice approaches.
DCH radio
Iu-cs
CS core
RNC
BTS
Radio network
UE
HSPA radio
HSPA flow
Iu-ps
PS core
RNC
BTS
Radio network
UE
HSPA radio
UE
DCH flow
HSPA flow
RNC
BTS
Radio network
Iu-cs
CS core
Figure 6. Illustration of CSoHS relation to IMS Voice and traditional CS voice
(Note “BTS” synonymous with “NodeB” in HSPA)
Page 7
IMS voice will allow operators to increase system capacity even further than with CSoHS, while permitting
the consolidation of their infrastructure on an IP based platform and enabling innovative new applications
B,C
that combine voice with data functions in the packet domain.
D. VOICE OVER LTE
Long Term Evolution (LTE) consists of a radio access network called the Evolved UMTS Radio Access
Network (E-UTRAN), and packet core network called Evolved Packet Core (EPC), together referred to as
the Evolved Packet System (EPS). The principal drivers for LTE have been to provide higher bandwidth
at the radio interface, and better spectral efficiency (the information rate transmitted over a given
bandwidth) and lower latency for packet data. LTE was first standardized in the 3GPP Rel-8
specifications.
Support for voice in the EPS can be done with IP Multimedia Subsystem (IMS) or CS Fallback (CSFB).
CSFB allows the UE to switch to GSM/HSPA CS services from LTE whenever voice services are needed.
On the other hand, Voice over LTE (“VoLTE”) encompasses native support for voice telephony over the
LTE radio access, and is achieved via IMS functionality.
IMS has many options and capabilities. In order to define some level of interoperability between the
capabilities offered by the device manufacturer and network vendors, GSMA established a profile in IR 92
D
for offering IMS voice (as well as SMS) over LTE.
As will be described further below, the efforts
expended to establish the IR 92 guidelines have also served as the foundation for developing a similar
set of guidelines for delivering an interoperable, IMS based voice service over HSPA.
Page 8
III.
BENEFITS OF VOICE OVER HSPA
Recent simulations substantiate the benefits anticipated from VoHSPA. Chief among these are increases
in the spectral efficiency of mobile networks. Spectral efficiency is a measure of how much can be
“packed” into a given unit of capacity for a given unit of time (and is typically measured in bits/second/Hz).
The logic is that if voice calls can be more efficiently delivered from a spectral standpoint over PS rather
than CS networks, then this frees up radio resources for additional data.
This is the case whether the technique deployed is CS voice over HSPA or IMS Voice, as summarized in
the following graphic.
Figure 7. VoHSPA Frees Up Resources for Data (Source: Qualcomm)
E
Simulations involving HSDPA as well as Rel-7 and Rel-8 systems support the potential for significant
resource gains with VoHSPA. For example:



A 2011 simulation analyzing the capacity of CSoHS using an HSPA Rel-7 system using
discontinuous reception and transmission (described further on in this paper) for best power
consumption savings showed results of 190 users/cell with dual antenna UEs, compared to 180
F
users per cell when those features were not used.
A 2010 simulation of CSoHS using an HSPA Rel-7/8 system showed significant in voice capacity
over Rel-99 CS voice under similar system conditions and voice quality, maxing out at better than
G
triple the capacity when equalizers are used in UEs rather than RAKE receivers.
A 2010 evaluation of Rel-8 Enhanced Serving Cell Change functionality (described later in this
paper) concluded that when implemented robust mobility for VoHSPA can be achieved,
Page 9
chronicling that under tough urban canyon conditions, significant gains are achieved compared to
H
legacy procedures in call drop rates, packet drops, and duration of serving cell changes.
Earlier studies provide additional evidence of the prospects for battery life gains when certain features
I
are enabled in the UE.
Page 10
VOHSPA TECHNICAL OPTIONS
IV.
A. IR.58 MINIMUM MANDATORY FEATURE SET
GSMA has recently completed a profile for devices and networks offering IMS Voice in its IR 58
F
Permanent Reference Document (PRD). This profile was developed to complement to the GSMA’s
establishment of a profile for the provision of VoLTE in it IR 92 PRD. IR 58 was developed by a global
cross section from industry to provide guidance on a minimum mandatory set of features defined in
existing Rel-8 specifications that should be implemented in order to ensure an interoperable, high quality,
IMS-based telephony service over an HSPA radio access layer.
IR 58 serves as an important point of departure for elaborating on the two technical options for
implementing VoHSPA. Below we outline the non-radio and radio features in IR 58 necessary for IMS
Voice. Immediately following, we build on that work to outline certain additional features we advise for
ensuring a robust VoHSPA service, based on either IMS Voice or CSoHS techniques.
1. NON-RADIO FEATURES
IR 58 outlines a number of non-radio features that should implemented in providing IMS Voice. These
are included in Sections 2, 3 and 5 of the PRD, and include the following basic features:



Generic IMS features (SIP registration, Authentication, Call establishment and termination, etc.)
IMS Media
Other Functionalities (IPv4/IPv6,, Emergency Services, Roaming, etc.)
More details are provided in the relevant sections of IR 58.
2. RADIO (AND RELATED PACKET CORE) FEATURES
Section 4 of IR 58 describes the minimum radio and relevant packet core features required for
IMS Voice. The key feature sets are described below.

Robust Header Compression (RoHC)
RTP/UDP/IP headers add significant overhead to VoIP payloads. (The AMR 12.2 full
rate frame size, for example, is 244 bits; RTP/UDP/IPv6 headers are 480 bits). Thus, it is
essential to use a header compression scheme such as RoHC. RoHC provides a high
degree of compression while still being very robust to packet drops. With VoIP headers,
RoHC is able to compress the RTP/UDP/IP headers down to 3 or 4 bytes a large
H
percentage of the time.

HSPA Radio Capabilities

Radio Bearers
Page 11
The data information in a voice call is split in two parts, signaling information and the content
of the voice communication. These have different Quality of Service (QoS) requirements.
While signaling information represents a small fraction of the total payload, it is sensitive to
data loss. On the other hand, voice content can cope with data loss, but is highly sensitive to
delay.
Due to these varying requirements, signaling information and voice payload are transported
over separate Packet Data Protocol (PDP) contexts, and ultimately different radio bearers
with special transport and priority settings, according to their profiles.
Given that voice payload is highly sensitive to delay but can accommodate a certain error
rate without significant degradation, the transport of voice packets makes use of a special
configuration of the Radio Link Control (RLC) protocol – unacknowledged mode (UM) – and
certain QoS priorities to ensure timely delivery. The use of RLC UM improves the delivery
speed by eliminating retransmission of packets with errors with which the human ear can
cope relatively well (up to a certain error rate). Furthermore, the use of the highest QoS
priority (‘Conversational’) ensures that packet schedulers will consider the delay sensitivity of
the packets and will transmit these in a timely manner even in cases of network congestion.
On the other hand, the signaling information required to perform call control functions (such
as establishing and terminating the call) is carried over a transport bearer in RLC
acknowledged mode (AM), to ensure an error-free delivery of the signaling messages. As
speed of delivery is not as critical here, the chosen QoS Traffic Class (TC) is “Interactive,”
with Traffic Handling Priority (THP) of “1,” which provides for medium prioritization.

UE Discontinuous Reception (DRX) and
DPCH (F-DPCH)
Discontinuous Transmission (DTX);
Fractional
UE DTX and DRX allow dynamically switching the UE’s transmitter off whenever there is no
actual data traffic to be sent in the uplink (UL). These modes also allow dynamically turning
the UE’s receiver off whenever there is no data traffic or UL power control to be received in
the downlink (DL). The obvious benefit of turning off transmitters and receivers consists of UE
battery conservation, yielding improved talk/stand-by times. A not-so-obvious benefit from
turning off the transmitter is to reduce interference from pilot and control-channel-only
transmissions, which reduce the UL capacity needed to support a voice user. This, in turn,
allows for supporting either a greater number of voice users, or for a greater portion of UL
capacity to be available for best efforts data users while serving the same number of voice
users.
UE DTX and DRX can be used when the UL data traffic is mapped onto HSUPA and the DL
data traffic on HSDPA. It was specifically designed with VoHSPA in mind, to provide for
efficient UE transmitter and receiver activity management during periods of speech inactivity,
as well as even enabling the transmitter to be turned off in between UL voice packets during
an active speech phase. UE DTX and DRX are Rel-7 features, introduced under the
Continuous Packet Connectivity (CPC) umbrella. J, K
Page 12
Fractional DPCH (F-DPCH) is a prerequisite for UE DTX & DRX operation, providing
improved UE battery life (better talk/stand-by times and increased system capacity) when
operated together with VoHSPA. The F-DPCH code resource is time-shared, thus several
users can share the same code space for power control information. F-DPCH allows
organizing all DL traffic on HSDPA in a code-efficient way by replacing the existing DL
DPCCH code dedicated for each UE with a 2-bit slot carrying the UL power control
commands. Each user receives an F-DPCH channel having one symbol per slot only, for
providing uplink power control commands, while ignoring the other nine symbols in each slot.
These remaining symbols are consequently allocated to provide power control commands to
other users.
F-DPCH is especially useful in conjunction with VoHSPA in that it allows for efficiently
supporting a large number of simultaneous voice users in the cell in a code-efficient manner.
F-DPCH is a Rel-6 feature, with additional improvements for soft handover support
introduced in Rel-7.

Conversational Traffic Class Handling
To ensure the quality of real-time services like VoIP under conditions of network congestion,
the network must be able to support a special QoS TC (Conversational) that provides certain
bitrate and delay guarantees. In HSPA, these parameters are indicated in the PDP context
with the Guaranteed Bitrate (GBR) and Transmission Delay parameters, which are mapped
down to the NodeB parameters GBR and Discard Timer, respectively.
In networks
supporting the Conversational TC, the Node-B scheduler has a special function to monitor
the current connection throughput and packet delay, and perform expedited transmission of
voice packets in case these parameters are not being met. In cases of network overload, the
NodeB may decide to drop voice packets that have not been transmitted in time.
The value of the GBR parameter should be set according to the bitrate requirements of the
Adaptive Multi-Rate (AMR) codec used (for instance, 23.84 kbps for AMR Wideband (AMRWB), 12.2 kbps for regular AMR Narrowband (AMR-NB) or 5.9 kbps for lower codec modes).
The Transmission Delay is measured between the UE and the edge of the network, and it
should be set to ensure a low enough mouth-to-ear delay (on the order of 100ms or lower).
Note that the use of GBR and delay sensitive schedulers, while necessary for a quality
delivery of voice and other real-time services, results in a certain capacity loss in the system
as compared to schedulers that work in best-effort mode.

Bearer Management
In order to assure the requisite QoS for IMS Voice, radio access bearers having the
appropriate characteristics must be established. For SIP signaling, the UE must establish a
Packet Data Network (PDN) connection by activating a PDP context with the Interactive TC
with THP setting of 1. For voice calls utilizing Conversational TC handling, the network must
establish a PDP context, using interaction with dynamic Policy Control & Charging (PCC)
functionality.
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
P-CSCF
The UE and the packet core must support the procedures for Proxy-Call Session Control
Function (P-CSCF) discovery via GSM and UMTS radio access networks, as described in the
M
relevant 3GPP specifications.

Inter-RAT Mobility
If the UE supports both HSPA and LTE, and both the HSPA and LTE networks support IMS
Voice, then the UE and the network shall support inter-Radio Access Technology (inter-RAT)
PS handovers to and from LTE. PS handover allows extended usage of IMS Voice over the
larger coverage provided by the LTE and HSPA layers, and minimizes the use of Single
Radio-Voice Call Continuity (SR-VCC).
B. ADDITIONAL FEATURES
4G Americas advises implementation of the following additional features b for VoHSPA. These features
are over and above the minimum mandatory features in IR 58, and unless otherwise noted, are advisable
for both IMS Voice and CSoHS. The basic motivations for these recommendations are to further
minimize packet losses and variations in packet arrival times that can impair the quality of voice
communications.
Required

De-Jitter Buffer (CSoHS only)
A de-jitter buffer at the RNC is required for the CSoHS approach. This is because voice packets
may arrive at the RNC from a UE with jitter on the UL, which means that the inter-arrival times of
packets is not constant. Jitter can also occur in soft-handover situations where the transmission
delay from each NodeB to a particular RNC varies. The RNC will use information in the packet
headers to identify the correct order and timing of the voice frames. The RNC transmits the output
of the de-jitter buffer to the MSC synchronously over the IuCS interface, as is done for a CS call.
The UE also implements the de-jitter buffer to remove jitter on the DL, which can result from
G
factors such as network loading.
Recommended

Bicasting
In HSDPA operation, during the Serving Cell Change (SCC) procedure from an old to a new
serving High-Speed Downlink Shared Channel (HS-DSCH) cell, all packets residing on the old
serving HS-DSCH cell are dropped for RLC UM bearers. In Rel-6, in order to optimize HSDPA
Page 14
operation for real-time traffic, a feature was introduced that allows bicasting of RLC UM Packet
Data Units (PDUs) from the RNC to both the old and the new HS-DSCH serving cells when
needed.
This feature minimizes the amount of packet loss during the SCC procedure, and is particularly
important for real-time traffic such as voice, which is transported over RLC UM and hence cannot
be recovered. Such packet losses can create audible impairments during HS-DSCH SCC
procedures. Note, however, that in severe urban canyon scenarios, bicasting alone cannot
recover all dropped packets, and in these cases, an Enhanced SCC (E-SCC) procedure is
H
recommended.

Enhanced Serving Cell Change
In the Enhanced-SCC (E-SCC) procedure standardized in Rel-8, a High Speed Shared Control
Channel (HS-SCCH) order from the target cell is used for indicating an SCC to the UE. In this
procedure, for a short period of time the UE has to monitor the HS-SCCH channel from the target
cell while also simultaneously monitoring the HS-SCCH channel and decoding data from the
source cell.
In the E-SCC procedure, the network pre-configures the UE with serving cell related information.
In the legacy SCC procedure, by contrast, such information is received only as part of the RLC
reconfiguration message that prompts an SCC, and whose reception in urban canyon scenarios
can be unreliable. The pre-configured information at the UE also includes the particular HSSCCH channel (i.e., channelization code) that the UE needs to monitor for the target cell. At the
appropriate time, the target cell will send an indication of its readiness on the HS-SCCH channel
being monitored by the UE. Upon receiving this indication, the UE changes its serving cell to the
H
target cell, and applies the pre-configured information stored for the target cell.

HS-SCCH-less operation
In typical HSDPA operation, the network indicates to the UE that there is a packet for it using HSSCCH, while the actual packet is sent over the HS-PDSCH data channel(s). For relatively small
packets, such as with voice, the overhead from the HS-SCCH can take a significant portion of the
overall transmit power needed to deliver that packet. In addition, for large numbers of
simultaneous VoHSPA users, the HS-SCCH channel utilization in the cell will be very high
compared to delivering the equivalent amount of data to high data rate (non-voice) users. This
increased ratio of HS-SCCH usage per bits delivered for voice may lead the cell occasionally to
deplete its HS-SCCH capacity.
HS-SCCH-less operation allows for transmitting a voice packet without the HS-SCCH indication,
eliminating the overhead from the initial packet transmission attempt completely. The UE will
continue receiving on the assigned HS-PDSCH data channel if there is a voice packet for it,
without the aid of HS-SCCH indicating when it is there. Higher data rates or retransmissions of
missed voice packets are still scheduled with HS-SCCH. This feature is referred to “Reduced
L
complexity HS-SCCH-less operation” in the 3GPP specifications.
Page 15

Voice Call Continuity (IMS Voice only)
For IMS Voice, an operator may encounter deployment scenarios where its IMS Voice capable
radio coverage may not be coextensive with its concurrent CS radio coverage. In such scenarios,
complementing IMS Voice coverage with CS capable coverage may prove advisable. The
Single-Radio Voice Call Continuity (VCC) procedures provided in the 3GPP specifications define
N,O
procedures for IMS Voice handovers between HSPA and UMTS/GSM CS coverage.
A concluding note applies for both CSoHS and IMS Voice, and relates less to the specific feature
identified above, but is a more general observation about the scheduler enhancements needed at the
RNC to ensure robust mobility. Preserving seamless connections during mobility, and mapping voice
and control signaling to HSDPA entail tighter requirements for SCC performance than with traditional
configurations of voice and signaling. As discussed in several places earlier in this paper, the RNC
scheduler needs to be QoS aware in order to properly manage the special conversational TC
requirements. In addition, the scheduler needs to apply a special TC handling to the signaling messages
in order to guarantee that for example the commands ordering the UE to change its serving cell are
received with very high reliability and minimal latency. Furthermore, the network algorithms related to
SCC procedures may require adjusting, as more aggressive approaches to deciding on the serving cell,
minimizing the execution time and eliminating related connection breaks on the cell change may be
required with a voice connection than what is permissible for more delay tolerant services.
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V.
STATUS OF VOHSPA REALIZATION
As part of 4G Americas’ efforts to complete this report, vendors provided information about when
VoHSPA features would be available from them. “Availability” in this case means when these features
are available to mobile network operators for testing and validation. Vendor responses were aggregated
in order to arrive at the timelines given in the Feature Availability Matrix below.
The features listed parallel those described in the prior section of the paper. In the first grouping, the IR
58 minimum mandatory features necessary for IMS Voice are listed. The second grouping consists of the
additional features that 4G Americas recommends for a high quality VoHSPA service (whether based on
CSoHS or IMS Voice). Corresponding references to IR 58 are provided as appropriate in the last column.
Table 1. Feature Availability Matrix
Availability
Feature
IMS Voice
IR 58
Reference
A. N/A
A. 1Q2012
A. Sec. 2
B. N/A
B. 1Q2012
B. Sec. 3
C. N/A
C. 1Q2012
C. Sec. 5
A. RoHC (IMS Voice only)
A. N/A
A. 2Q2012-EY2013
A. Sec. 4.1
B. HSPA Radio Capabilities
B. 1Q2012-
B. 1Q2012-EY2012
B. Sec. 4.2
CSoHS
IR 58 Minimum
Mandatory Features
Non-Radio Features
A. Generic IMS features (SIP
registration, authentication, call
establishment and termination, etc.)
B. IMS Media
C. Other functionalities (IPv4 & v6,
Emergency Services, Roaming, etc.)
Radio (& related packet core) features
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C. Bearer Management
EY2013
C. 2H2012
C. Sec. 4.3
D. P-CSF Discovery
C. 2H2012
D. 1Q2012
D. Sec. 4.4
E. Inter-RAT Mobility
D. N/A
E. 2H2012-EY2013
E. Sec. 4.5
A. 1Q2012EY2013
A. N/A
A. N/A
A. Bicasting
A. No plans
A. No plans
A. N/A
B. E-SCC
B. 2Q2013EY2013
B.2Q2013-EY2013
B. N/A
E. 2H2012EY2013
Additional Features
Mandatory
A. De-jitter Buffer(CSoHS only)
Recommended
C. 2013
C. HSSCCH-less operation
C. 2013
C. N/A
D. 2013
D. VCC (IMS Voice only)
D. N/A
D. N/A
As outlined above, vendors have indicated that the minimum mandatory features needed for IMS Voice
are either available at the present time, or will be available later this year or in 2013. In addition, many of
the additional features recommended by 4G Americas either are or will be available along the same
timescales, with the notable exception of bicasting enhancements.
The time estimates listed above are best-estimate summary information, and should not be construed as
contractual information or specific to any commercial arrangement. Each individual vendor within 4G
Americas and the industry as a whole will have their own specific availability dates for the listed features.
The timeframes above are intended to provide an overall sense for feature readiness.
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CONCLUSION
VI.
In general, it should be apparent that that full realization of VoHSPA will involve a number of interrelated
dependencies. These include important initiatives in the following areas:







Standardization developments
Terminal enhancements
Radio access infrastructure enhancements
Interworking with legacy CS networks and technologies
Coexistence and roaming with emerging LTE networks
Maturation of the IMS ecosystem
Continued diffusion of HSPA technology
The graphic below encapsulates these considerations.
LTE coexistence
and roaming
HSPA
technology
diffusion
Standards
Interworking
with legacy CS
technology
VoHSPA
development
Terminal
enhancements
IMS ecosystem
maturation
Infrastructure
enhancements
Figure 8. Key Interrelated Dependencies for VoHSPA
A key finding in this paper is that virtually all of the features believed necessary for a robust VoHSPA
service are either presently available or will be available from vendors later this year or in 2013 for testing
and validation. The sole exception pertains to bicasting.
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Further, the industry will continue to remain mindful of the need to ensure that certain critical features
remain fully functional. For example, IR 58 contains provisions defining the IMS Emergency Service
features that will enable emergency calling services expected by consumers.
Finally, with respect to the important work concluded by GSMA in IR 58, further efforts will need to be
pursued within GSMA to ensure the effective cross-operation of those guidelines with other GSMA PRDs
P,Q
such as IR.64 IMS Centralized Services (ICS) and IR.65 IMS Roaming.
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REFERENCES
A. 3GPP TSG Service and Systems Aspects, 3rd Generation Mobile System Release 1999
Specifications, 3G TS 21.101 V3.0.0 (2000-03)
http://www.3gpp.org/ftp/tsg_sa/WG3_Security/_Specs/33908-300.pdf
B. 4G Americas, Evolution of HSPA (2011)
http://www.4gamericas.org/documents/4G%20Americas%20White%20Paper_The%20Evolution%20of%2
0HSPA_October%202011x.pdf
C. 4G Americas, Mobile Broadband Explosion (2011)
http://www.4gamericas.org/documents/Mobile%20Broadband%20Explosion_Rysavy_Sept2011.pdf
D. IMS profile for Voice and SMS (GSMA permanent reference document IR 92.1.0)
http://www.gsma.com/go/download/?file=ir.92.pdf
E. Qualcomm, How to Meet Data Demand (2011)
http://www.qualcomm.com/media/documents/files/how-to-meet-data-demand-.pdf
F. Qualcomm, CSoHS Voice Capacity in HSPA Networks (2011)
http://www.qualcomm.com/media/documents/files/csohs-voice-capacity-in-hspa-networks-with-realisticoverhead-channel-modeling.pdf
G. Qualcomm, Circuit-Switched Voice Services over HSPA (2010)
http://www.qualcomm.com/documents/circuit-switched-cs-voice-services-over-hspa
H. Qualcomm, Enhanced HSDPA Mobility Performance (2010)
http://www.qualcomm.com/documents/enhanced-hsdpa-mobility-performance-quality-and-robustnessvoip-service)
I. Tapia et al, HSPA Performance & Evolution, Wiley (2009)
J. IMS Profile for Voice over HSPA (GSMA permanent reference document IR. 58.1.0)
http://www.gsma.com/documents/ir-58-1-0-ims-profile-for-voice-over-hspa/21986
K. Qualcomm, Performance of VoIP Services over 3GPP WCDMA Networks (2008)
http://www.qualcomm.com/documents/performance-voip-services-over-3gpp-wcdma-networks
L. 3GPP, TR25.903 -Technical Specification Group Radio Access Network; Continuous connectivity for
packet data users (Release 7) http://www.3gpp.org/ftp/Specs/archive/25_series/25.903/25903-700.zip
M. 3GPP, TS 24.229 - IP multimedia call control protocol based on Session Initiation Protocol (SIP) and
Session Description Protocol (SDP); Stage 3
http://www.3gpp.org/ftp/Specs/archive/24_series/24.229/24229-930.zip
N. 3GPP, TS 23.216 - Single Radio Voice Call Continuity (SRVCC); Stage 2
http://www.3gpp.org/ftp/Specs/archive/23_series/23.216/23216-870.zip
O. 3GPP, TS 23.237 - IP Multimedia Subsystem (IMS) Service Continuity; Stage 2
http://www.3gpp.org/ftp/Specs/archive/23_series/23.237/23237-870.zip
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P. GSMA, IR.64.20- IMS Service Centralization and Continuity Guidelines
http://www.gsma.com/go/download/?file=ir6420.pdf
Q. GSMA, IR 65.5.0 - IMS Roaming and Interworking Guidelines
http://www.gsma.com/go/download/?file=ir6550.pdf
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ABBREVIATIONS
3GPP
AM
AMR
AMR-NB
AMR-WB
APN
BTS
CDMA
CPC
CS
CSFB
CSoHS
DCH
DL
DRX
DTX
EPC
EPS
E-SCC
E-UTRAN
F-DPCH
GBR
GSM
GSMA
HS-DSCH
HS-SCCH
HSDPA
HSPA
HSUPA
IMS
IP
IPv4
IPv6
IR
LTE
MS
NodeB
PCC
3rd Generation Partnership Project
Acknowledged Mode
Adaptive Multi-Rate
AMR Narrowband
AMR Wideband
Access Point Name
Base Transceiver Station
Code Division Multiple Access
Continuous Packet Connectivity
Circuit-Switched
CS Fallback
CS Voice over HSPA
Dedicated Transport Channel
Downlink
Discontinuous Reception
Discontinuous Transmission
Enhanced Packet Core
Enhanced Packet System (i.e., LTE + EPC)
Enhanced Service Cell Change
Enhanced UMTS Radio Access Network (a/k/a LTE)
Fractional Dedicated Physical Channel
Guaranteed Bit Rate
Global System for Mobile Communications
Global organization for 3GPP technologies, f/k/a GSM Association
High-Speed Downlink Shared Channel
High-Speed Shared Control Channel
High-Speed Downlink Packet Access
High-Speed Packet Access
High-Speed Uplink Packet Access
IP Multimedia Subsystem
Internet Protocol
IP version 4
IP version 6
International Roaming (a GSMA document citation tool)
Long Term Evolution
Mobile Station
Base Station in HSPA networks
Policy and Charging Control
P-CSCF
PDN
PDP
PDU
PRD
PS
QoS
RAB
RAT
RLC
RoHC
Proxy - Call Session Control Function
Packet Data Network
Packet Data Protocol
Packet Data Unit
Permanent Reference Document (a GSMA document citation tool)
Packet-Switched
Quality of Service
Radio Access Bearer
Radio Access Technology
Radio Link Control
Robust Header Compression
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RRC
RTCP
RTP
SCC
SIP
SR-VCC
TDMA
THP
UDP
UE
UL
UM
UMTS
UTRAN
VoHSPA
VoIP
W-CDMA
Radio Resource Control
RTP Control Protocol
Real-Time Protocol
Serving Cell Change
Session Initiation Protocol
Single Radio Voice Call Continuity
Time Division Multiple Access
Traffic Handling Priority
User Datagram Protocol
User Equipment
Uplink
Unacknowledged Mode
Universal Mobile Telecommunications System
UMTS Terrestrial Radio Access Network
Voice over HSPA (using either Circuit-Switched or IMS approaches)
Voice Over IP (typically refers in this paper to IMS Voice over HSPA)
Wideband CDMA
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ACKNOWLEDGEMENTS
The mission of 4G Americas is to promote, facilitate and advocate for the deployment and adoption of the
3GPP family of technologies throughout the Americas. 4G Americas' Board of Governor members include
Alcatel-Lucent, América Móvil, AT&T, Cable & Wireless, CommScope, Ericsson, Gemalto, HP, Huawei,
Nokia Siemens Networks, Openwave, Powerwave, Qualcomm, Research In Motion (RIM), Rogers, TMobile USA and Telefónica.
4G Americas would like to recognize the significant project leadership and important contributions of Bob
Calaff of T-Mobile USA, as well as the contributions of Etienne Chaponniere of Qualcomm, and Karri
Ranta-Aho and Curt Wong of Nokia Siemens Networks, as well as representatives from the other
member companies on 4G Americas’ Board of Governors who participated in the development of this
white paper.
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