4g americas vohspa paper_final 2 22 12

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

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.

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)

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.

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.

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 established in version 3.0.0 of 3GPP Rel-99.A 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.

GSM BTS

2/3G MSC/VLR

PSTN

Abis Air (Um)

BSC A SS7

RNC Iu-cs

NodeB

Iub Air (Uu)

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 CSoHS, as will be explained further below.P

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.

Figure 6. Illustration of CSoHS relation to IMS Voice and traditional CS voice (Note “BTS” synonymous with “NodeB” in HSPA)

IuCS

IuPS

RNC

CS R99

AMR adapt.

Transportqueues etc

HSPA

PS R99

NodeB

HSPA schedulerCombined to one carrier

AMR adaptation possible

CS mapped to R99 or HSPA bearer depending on terminal capability

Scheduler prioritizesvoice packets

CS

voic

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SPA

Trad

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Svo

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over

DC

HTr

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Voic

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RNC CS coreBTSUE

Iu-cs

Radio network

DCH flowDCH radio

RNC PS coreBTSUE

Iu-ps

Radio network

HSPA flowHSPA radio

RNC CS coreBTSUE

Iu-cs

Radio network

HSPA flowHSPA radio

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 that combine voice with data functions in the packet domain. B,C

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 for offering IMS voice (as well as SMS) over LTE.D 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.

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 users per cell when those features were not used.F

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 triple the capacity when equalizers are used in UEs rather than RAKE receivers.G

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,

chronicling that under tough urban canyon conditions, significant gains are achieved compared to legacy procedures in call drop rates, packet drops, and duration of serving cell changes.H

Earlier studies provide additional evidence of the prospects for battery life gains when certain features are enabled in the UE.I

IV. VOHSPA TECHNICAL OPTIONS

A. IR.58 MINIMUM MANDATORY FEATURE SET

GSMA has recently completed a profile for devices and networks offering IMS Voice in its IR 58 Permanent Reference Document (PRD). F 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 percentage of the time.H

HSPA Radio Capabilities

Radio Bearers

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 Discontinuous Transmission (DTX); Fractional

DPCH (F-DPCH)

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

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 (AMR-WB), 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.

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 relevant 3GPP specifications.M

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 factors such as network loading.G

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

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 recommended.H

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 HS-SCCH 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 target cell, and applies the pre-configured information stored for the target cell.H HS-SCCH-less operation

In typical HSDPA operation, the network indicates to the UE that there is a packet for it using HS-SCCH, 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 complexity HS-SCCH-less operation” in the 3GPP specifications.L

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 procedures for IMS Voice handovers between HSPA and UMTS/GSM CS coverage.N,O

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.

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

Feature

Availability

CSoHS IMS Voice IR 58 Reference

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.)

A. N/A

B. N/A

C. N/A

A. 1Q2012

B. 1Q2012

C. 1Q2012

A. Sec. 2

B. Sec. 3

C. Sec. 5

Radio (& related packet core) features

A. RoHC (IMS Voice only)

B. HSPA Radio Capabilities

A. N/A

B. 1Q2012-

A. 2Q2012-EY2013

B. 1Q2012-EY2012

A. Sec. 4.1

B. Sec. 4.2

C. Bearer Management

D. P-CSF Discovery

E. Inter-RAT Mobility

EY2013

C. 2H2012

D. N/A

E. 2H2012-EY2013

C. 2H2012

D. 1Q2012

E. 2H2012-EY2013

C. Sec. 4.3

D. Sec. 4.4

E. Sec. 4.5

Additional Features Mandatory A. De-jitter Buffer(CSoHS only) Recommended A. Bicasting B. E-SCC C. HSSCCH-less operation D. VCC (IMS Voice only)

A. 1Q2012-EY2013 A. No plans B. 2Q2013-EY2013 C. 2013 D. N/A

A. N/A A. No plans B.2Q2013-EY2013 C. 2013 D. 2013

A. N/A A. N/A B. N/A C. 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.

VI. CONCLUSION

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.

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.

VoHSPA

LTE coexistence and roaming

Interworking with legacy CS

technology

IMS ecosystem maturation

Infrastructure enhancements

Terminal enhancements

Standards development

HSPA technology

diffusion

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 such as IR.64 IMS Centralized Services (ICS) and IR.65 IMS Roaming. P,Q

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%20HSPA_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-realistic-overhead-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-robustness-voip-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 3rd Generation Partnership Project AM Acknowledged Mode AMR Adaptive Multi-Rate AMR-NB AMR Narrowband AMR-WB AMR Wideband APN Access Point Name BTS Base Transceiver Station CDMA Code Division Multiple Access CPC Continuous Packet Connectivity CS Circuit-Switched CSFB CS Fallback CSoHS CS Voice over HSPA DCH Dedicated Transport Channel DL Downlink DRX Discontinuous Reception DTX Discontinuous Transmission EPC Enhanced Packet Core EPS Enhanced Packet System (i.e., LTE + EPC) E-SCC Enhanced Service Cell Change E-UTRAN Enhanced UMTS Radio Access Network (a/k/a LTE) F-DPCH Fractional Dedicated Physical Channel GBR Guaranteed Bit Rate GSM Global System for Mobile Communications GSMA Global organization for 3GPP technologies, f/k/a GSM Association HS-DSCH High-Speed Downlink Shared Channel HS-SCCH High-Speed Shared Control Channel HSDPA High-Speed Downlink Packet Access HSPA High-Speed Packet Access HSUPA High-Speed Uplink Packet Access IMS IP Multimedia Subsystem IP Internet Protocol IPv4 IP version 4 IPv6 IP version 6 IR International Roaming (a GSMA document citation tool) LTE Long Term Evolution MS Mobile Station NodeB Base Station in HSPA networks PCC Policy and Charging Control P-CSCF Proxy - Call Session Control Function PDN Packet Data Network PDP Packet Data Protocol PDU Packet Data Unit PRD Permanent Reference Document (a GSMA document citation tool) PS Packet-Switched QoS Quality of Service RAB Radio Access Bearer RAT Radio Access Technology RLC Radio Link Control RoHC Robust Header Compression

RRC Radio Resource Control RTCP RTP Control Protocol RTP Real-Time Protocol SCC Serving Cell Change SIP Session Initiation Protocol SR-VCC Single Radio Voice Call Continuity TDMA Time Division Multiple Access THP Traffic Handling Priority UDP User Datagram Protocol UE User Equipment UL Uplink UM Unacknowledged Mode UMTS Universal Mobile Telecommunications System UTRAN VoHSPA

UMTS Terrestrial Radio Access Network Voice over HSPA (using either Circuit-Switched or IMS approaches)

VoIP Voice Over IP (typically refers in this paper to IMS Voice over HSPA) W-CDMA Wideband CDMA

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, T-Mobile 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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