TABLE OF CONTENTSEXECUTIVE SUMMARY ..........................................................................................
EXECUTIVE SUMMARYOver the next few years HSPA will be, based simply on sheer projected number of devices, theoverwhelming ...
I.      THE GROWTH OF HSPAGlobally, as of February 1, there were 423 HSPA networks in 160 countries in operation. And base...
These trends have some important implications. One relates to the evolutionary path for mobile voicetelephony service, whi...
II.      EVOLUTION OF VOICE SERVICE OVER 3GPP MOBILE NETWORKS        A. GSM CS VOICECellular service based on GSM technolo...
GSM BTS                                                          PSTN                                                   A ...
Scheduler prioritizes             CS mapped to R99 or HSPA bearer          AMR adaptation                        voice pac...
IMS voice will allow operators to increase system capacity even further than with CSoHS, while permittingthe consolidation...
III.       BENEFITS OF VOICE OVER HSPARecent simulations substantiate the benefits anticipated from VoHSPA. Chief among th...
chronicling that under tough urban canyon conditions, significant gains are achieved compared to                          ...
IV.       VOHSPA TECHNICAL OPTIONS          A. IR.58 MINIMUM MANDATORY FEATURE SETGSMA has recently completed a profile fo...
The data information in a voice call is split in two parts, signaling information and the content    of the voice communic...
Fractional DPCH (F-DPCH) is a prerequisite for UE DTX & DRX operation, providing    improved UE battery life (better talk/...
   P-CSCF           The UE and the packet core must support the procedures for Proxy-Call Session Control           Funct...
operation for real-time traffic, a feature was introduced that allows bicasting of RLC UM PacketData Units (PDUs) from the...
   Voice Call Continuity (IMS Voice only)       For IMS Voice, an operator may encounter deployment scenarios where its I...
V.       STATUS OF VOHSPA REALIZATIONAs part of 4G Americas’ efforts to complete this report, vendors provided information...
C. Bearer Management                            EY2013             C. 2H2012                 C. Sec. 4.3D. P-CSF Discovery...
VI.       CONCLUSIONIn general, it should be apparent that that full realization of VoHSPA will involve a number of interr...
Further, the industry will continue to remain mindful of the need to ensure that certain critical featuresremain fully fun...
REFERENCESA. 3GPP TSG Service and Systems Aspects, 3rd Generation Mobile System Release 1999Specifications, 3G TS 21.101 V...
P. GSMA, IR.64.20- IMS Service Centralization and Continuity Guidelineshttp://www.gsma.com/go/download/?file=ir6420.pdfQ. ...
ABBREVIATIONS3GPP            3rd Generation Partnership ProjectAM              Acknowledged ModeAMR             Adaptive M...
RRC      Radio Resource ControlRTCP     RTP Control ProtocolRTP      Real-Time ProtocolSCC      Serving Cell ChangeSIP    ...
ACKNOWLEDGEMENTSThe mission of 4G Americas is to promote, facilitate and advocate for the deployment and adoption of the3G...
Delivering Voice over HSPA
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Delivering Voice over HSPA

  1. 1. TABLE OF CONTENTSEXECUTIVE SUMMARY .............................................................................................................................. 2I. THE GROWTH OF HSPA ...................................................................................................................... 3II. 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 .................................................................................................................................... 8III. BENEFITS OF VOICE OVER HSPA ...................................................................................................... 9IV. 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 ............................................................................................................................. 14V. STATUS OF VoHSPA REALIZATION.................................................................................................. 17VI. CONCLUSION ...................................................................................................................................... 19REFERENCES ............................................................................................................................................ 21ABBREVIATIONS ....................................................................................................................................... 23ACKNOWLEDGEMENTS ........................................................................................................................... 25 Page 1
  2. 2. EXECUTIVE SUMMARYOver the next few years HSPA will be, based simply on sheer projected number of devices, theoverwhelming technology for delivering mobile broadband technology to consumers. The consensus isthat 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 facetof this effort relates to the delivery of voice services. Up to now, mobile voice services have beendelivered by service providers using traditional circuit-switched (CS) technology. Largely absent havebeen the benefits to be derived from leveraging packet-switched (PS) and Internet Protocol (IP) basedtechnologies 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. Oncedeployed, both mobile network operators and consumers stand to benefit significantly from moreinnovative, 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 IPMultimedia Subsystem (IMS) technology developed in conjunction with Long Term Evolution (LTE), and isreferred to as IMS Voice over HSPA or simply IMS Voice. The other option delivers voice by modifyingexisting circuit-switch based techniques so that those communications can be transmitted over an HSPAinfrastructure, and is referred to as CS Voice over HSPA (CSoHS).This paper reports on the status of the ecosystem for commercializing the needed technology featuresunder both options. As detailed later in the paper, with one exception, all of the features considerednecessary for a robust VoHSPA service are available now or will be available from vendors in 2012-2013for 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 makeVoHSPA a reality for consumers. Page 2
  3. 3. I. THE GROWTH OF HSPAGlobally, as of February 1, there were 423 HSPA networks in 160 countries in operation. And based onthe number of subscriptions, HSPA stands as the predominant means of providing mobile broadbandservices 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, ascompared 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 totalnumber of HSPA subscriptions will surpass the total number of GSM subscriptions in Latin America. Thisis depicted in the graph below. Figure 2. Latin American Technology Growth Forecast 2011-2016 (Source: Informa) Page 3
  4. 4. These trends have some important implications. One relates to the evolutionary path for mobile voicetelephony service, which has been one of, if not the most important service provided over mobilenetworks, and up to the present, the main source of revenues for mobile operators. For example, willpreparations to deliver voice services over emerging LTE networks be leveraged to improve mobile voiceservice over existing mobile networks? And what provisions are being made so that legacy voice servicescan coexist and interoperate with newer voice services?The mobile industry is working to address these questions. In order to better appreciate thesedevelopments, some background is provided in the next section. Note that this information, and moregenerally this paper, deals with the evolution of mobile voice telephony services in 3GPP based mobilenetworks, that is, carrier grade telephony service provisioned by mobile operators, in contrast to over thetop (OTT) VoIP service provided by third parties over the operator’s network but without the involvementof the mobile operator itself in the service provision. Page 4
  5. 5. II. EVOLUTION OF VOICE SERVICE OVER 3GPP MOBILE NETWORKS A. GSM CS VOICECellular service based on GSM technology was launched in the early 1990s. Based on digital CStechnology to provide full duplex (simultaneous two way) voice telephony. GSM employs a dedicatedtimeslot over the air interface to carry individual voice communications from the Mobile Station (MS) to theBase Transceiver Station (BTS), transiting on from there toward the core network using dedicated trunkresources. 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 followingfigure illustrates the basic network elements for carrying GSM CS voice. Figure 3. Illustration of network elements for providing GSM CS voice B. UMTS CS VOICEUniversal Mobile Telecommunications System (UMTS) is a third generation mobile cellular technology fornetworks based on the GSM standard, and was first launched in the early 2000s. UMTS employsWideband Code Division Multiple Access (W-CDMA) radio access technology to offer greater spectralefficiency and bandwidth for both CS voice and PS data to mobile network operators than TDMA radioaccess offered with GSM. The core network supporting UMTS CS voice does not differ much from theone supporting GSM CS voice. This allows the UMTS and GSM radio access network to share a commoncore network as shown in the figure below. Page 5
  6. 6. GSM BTS PSTN A SS7 Abis BSC Air 2/3G (Um) MSC/ VLR Iu-cs NodeB RNC Air (Uu) Iub Figure 4. Illustration of network elements for providing both UMTS and GSM CS voice service C. VOICE OVER HSPAThe 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 Aestablished 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 overHSPA (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 littledifference whether data bits flow over a CS or PS connection. Thus, in order to be able to benefit fromvoice related HSPA improvements, the limitation preventing CS connections from being mapped to theHSPA radio layer was removed in the Rel-8 specifications. (Notably the feature capability indication bitfor UE support of CSoHS was introduced in the Rel-7 specifications, making it “early implementable,” thatis, a Rel-7 compliant UE is able to support CSoHS even though the feature is technically part of Rel-8specifications.)The graphic below depicts CSoHS implementation. Page 6
  7. 7. Scheduler prioritizes CS mapped to R99 or HSPA bearer AMR adaptation voice packets depending on terminal capability possible Transport AMR queues etc adapt. CS R99 IuCS HSPA scheduler HSPA Combined to one carrier IuPS PS R99 NodeB RNC Figure 5. Illustration of CSoHS ImplementationIn CSoHS, the already digitized voice packets use HSPA channels for transport back to the existing CSinfrastructure 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 PCSoHS, as will be explained further below.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 MultimediaSubsystem (IMS) technology standardized in Rel-8. The graphic below highlights the distinctionsbetween traditional Rel-99 CS Voice, CSoHS and IMS Voice approaches. voice over DCH Traditional CS DCH radio Iu-cs DCH flow UE BTS RNC CS core Radio network Voice over IP over HSPA HSPA radio Iu-ps HSPA flow UE BTS RNC PS core Radio network over HSPA CS voice HSPA radio Iu-cs HSPA flow UE BTS RNC CS core Radio network Figure 6. Illustration of CSoHS relation to IMS Voice and traditional CS voice (Note “BTS” synonymous with “NodeB” in HSPA) Page 7
  8. 8. IMS voice will allow operators to increase system capacity even further than with CSoHS, while permittingthe consolidation of their infrastructure on an IP based platform and enabling innovative new applications B,Cthat combine voice with data functions in the packet domain. D. VOICE OVER LTELong Term Evolution (LTE) consists of a radio access network called the Evolved UMTS Radio AccessNetwork (E-UTRAN), and packet core network called Evolved Packet Core (EPC), together referred to asthe Evolved Packet System (EPS). The principal drivers for LTE have been to provide higher bandwidthat the radio interface, and better spectral efficiency (the information rate transmitted over a givenbandwidth) and lower latency for packet data. LTE was first standardized in the 3GPP Rel-8specifications.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 theLTE radio access, and is achieved via IMS functionality.IMS has many options and capabilities. In order to define some level of interoperability between thecapabilities offered by the device manufacturer and network vendors, GSMA established a profile in IR 92 Dfor offering IMS voice (as well as SMS) over LTE. As will be described further below, the effortsexpended to establish the IR 92 guidelines have also served as the foundation for developing a similarset of guidelines for delivering an interoperable, IMS based voice service over HSPA. Page 8
  9. 9. III. BENEFITS OF VOICE OVER HSPARecent simulations substantiate the benefits anticipated from VoHSPA. Chief among these are increasesin 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 ratherthan 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 inthe following graphic. E Figure 7. VoHSPA Frees Up Resources for Data (Source: Qualcomm)Simulations involving HSDPA as well as Rel-7 and Rel-8 systems support the potential for significantresource 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
  10. 10. 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 Iare enabled in the UE. Page 10
  11. 11. IV. VOHSPA TECHNICAL OPTIONS A. IR.58 MINIMUM MANDATORY FEATURE SETGSMA has recently completed a profile for devices and networks offering IMS Voice in its IR 58 FPermanent Reference Document (PRD). This profile was developed to complement to the GSMA’sestablishment of a profile for the provision of VoLTE in it IR 92 PRD. IR 58 was developed by a globalcross section from industry to provide guidance on a minimum mandatory set of features defined inexisting 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 forimplementing VoHSPA. Below we outline the non-radio and radio features in IR 58 necessary for IMSVoice. Immediately following, we build on that work to outline certain additional features we advise forensuring a robust VoHSPA service, based on either IMS Voice or CSoHS techniques.1. NON-RADIO FEATURESIR 58 outlines a number of non-radio features that should implemented in providing IMS Voice. Theseare 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 forIMS 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
  12. 12. 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 Page 12
  13. 13. 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. Page 13
  14. 14.  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 FEATURES4G Americas advises implementation of the following additional features b for VoHSPA. These featuresare over and above the minimum mandatory features in IR 58, and unless otherwise noted, are advisablefor both IMS Voice and CSoHS. The basic motivations for these recommendations are to furtherminimize packet losses and variations in packet arrival times that can impair the quality of voicecommunications.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
  15. 15. operation for real-time traffic, a feature was introduced that allows bicasting of RLC UM PacketData Units (PDUs) from the RNC to both the old and the new HS-DSCH serving cells whenneeded.This feature minimizes the amount of packet loss during the SCC procedure, and is particularlyimportant for real-time traffic such as voice, which is transported over RLC UM and hence cannotbe recovered. Such packet losses can create audible impairments during HS-DSCH SCCprocedures. Note, however, that in severe urban canyon scenarios, bicasting alone cannotrecover all dropped packets, and in these cases, an Enhanced SCC (E-SCC) procedure is Hrecommended. Enhanced Serving Cell ChangeIn the Enhanced-SCC (E-SCC) procedure standardized in Rel-8, a High Speed Shared ControlChannel (HS-SCCH) order from the target cell is used for indicating an SCC to the UE. In thisprocedure, for a short period of time the UE has to monitor the HS-SCCH channel from the targetcell while also simultaneously monitoring the HS-SCCH channel and decoding data from thesource 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 RLCreconfiguration message that prompts an SCC, and whose reception in urban canyon scenarioscan 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 theappropriate time, the target cell will send an indication of its readiness on the HS-SCCH channelbeing monitored by the UE. Upon receiving this indication, the UE changes its serving cell to the Htarget cell, and applies the pre-configured information stored for the target cell. HS-SCCH-less operationIn 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 smallpackets, such as with voice, the overhead from the HS-SCCH can take a significant portion of theoverall transmit power needed to deliver that packet. In addition, for large numbers ofsimultaneous VoHSPA users, the HS-SCCH channel utilization in the cell will be very highcompared to delivering the equivalent amount of data to high data rate (non-voice) users. Thisincreased ratio of HS-SCCH usage per bits delivered for voice may lead the cell occasionally todeplete 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 willcontinue 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 ofmissed voice packets are still scheduled with HS-SCCH. This feature is referred to “Reduced Lcomplexity HS-SCCH-less operation” in the 3GPP specifications. Page 15
  16. 16.  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 featureidentified above, but is a more general observation about the scheduler enhancements needed at theRNC to ensure robust mobility. Preserving seamless connections during mobility, and mapping voiceand control signaling to HSDPA entail tighter requirements for SCC performance than with traditionalconfigurations of voice and signaling. As discussed in several places earlier in this paper, the RNCscheduler needs to be QoS aware in order to properly manage the special conversational TCrequirements. In addition, the scheduler needs to apply a special TC handling to the signaling messagesin order to guarantee that for example the commands ordering the UE to change its serving cell arereceived with very high reliability and minimal latency. Furthermore, the network algorithms related toSCC 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 berequired with a voice connection than what is permissible for more delay tolerant services. Page 16
  17. 17. V. STATUS OF VOHSPA REALIZATIONAs part of 4G Americas’ efforts to complete this report, vendors provided information about whenVoHSPA features would be available from them. “Availability” in this case means when these featuresare available to mobile network operators for testing and validation. Vendor responses were aggregatedin 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 IR58 minimum mandatory features necessary for IMS Voice are listed. The second grouping consists of theadditional features that 4G Americas recommends for a high quality VoHSPA service (whether based onCSoHS or IMS Voice). Corresponding references to IR 58 are provided as appropriate in the last column. Table 1. Feature Availability Matrix Availability Feature CSoHS IMS Voice IR 58 ReferenceIR 58 MinimumMandatory FeaturesNon-Radio FeaturesA. Generic IMS features (SIP A. N/A A. 1Q2012 A. Sec. 2registration, authentication, callestablishment and termination, etc.) B. N/A B. 1Q2012 B. Sec. 3B. IMS Media C. N/A C. 1Q2012 C. Sec. 5C. Other functionalities (IPv4 & v6,Emergency Services, Roaming, etc.)Radio (& related packet core) featuresA. RoHC (IMS Voice only) A. N/A A. 2Q2012-EY2013 A. Sec. 4.1B. HSPA Radio Capabilities B. 1Q2012- B. 1Q2012-EY2012 B. Sec. 4.2 Page 17
  18. 18. C. Bearer Management EY2013 C. 2H2012 C. Sec. 4.3D. P-CSF Discovery C. 2H2012 D. 1Q2012 D. Sec. 4.4E. Inter-RAT Mobility D. N/A E. 2H2012-EY2013 E. Sec. 4.5 E. 2H2012- EY2013Additional FeaturesMandatoryA. De-jitter Buffer(CSoHS only) A. 1Q2012- A. N/A A. N/A EY2013RecommendedA. Bicasting A. No plans A. No plans A. N/AB. E-SCC B. 2Q2013- B.2Q2013-EY2013 B. N/A EY2013 C. 2013C. HSSCCH-less operation C. 2013 C. N/A D. 2013D. VCC (IMS Voice only) D. N/A D. N/AAs outlined above, vendors have indicated that the minimum mandatory features needed for IMS Voiceare either available at the present time, or will be available later this year or in 2013. In addition, many ofthe additional features recommended by 4G Americas either are or will be available along the sametimescales, with the notable exception of bicasting enhancements.The time estimates listed above are best-estimate summary information, and should not be construed ascontractual information or specific to any commercial arrangement. Each individual vendor within 4GAmericas 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. Page 18
  19. 19. VI. CONCLUSIONIn general, it should be apparent that that full realization of VoHSPA will involve a number of interrelateddependencies. 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 technologyThe graphic below encapsulates these considerations. LTE coexistence and roaming HSPA Interworking technology with legacy CS diffusion technology Standards VoHSPA IMS ecosystem development maturation Terminal Infrastructure enhancements enhancements Figure 8. Key Interrelated Dependencies for VoHSPAA key finding in this paper is that virtually all of the features believed necessary for a robust VoHSPAservice are either presently available or will be available from vendors later this year or in 2013 for testingand validation. The sole exception pertains to bicasting. Page 19
  20. 20. Further, the industry will continue to remain mindful of the need to ensure that certain critical featuresremain fully functional. For example, IR 58 contains provisions defining the IMS Emergency Servicefeatures 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 bepursued within GSMA to ensure the effective cross-operation of those guidelines with other GSMA PRDs P,Qsuch as IR.64 IMS Centralized Services (ICS) and IR.65 IMS Roaming. Page 20
  21. 21. REFERENCESA. 3GPP TSG Service and Systems Aspects, 3rd Generation Mobile System Release 1999Specifications, 3G TS 21.101 V3.0.0 (2000-03)http://www.3gpp.org/ftp/tsg_sa/WG3_Security/_Specs/33908-300.pdfB. 4G Americas, Evolution of HSPA (2011)http://www.4gamericas.org/documents/4G%20Americas%20White%20Paper_The%20Evolution%20of%20HSPA_October%202011x.pdfC. 4G Americas, Mobile Broadband Explosion (2011)http://www.4gamericas.org/documents/Mobile%20Broadband%20Explosion_Rysavy_Sept2011.pdfD. IMS profile for Voice and SMS (GSMA permanent reference document IR 92.1.0)http://www.gsma.com/go/download/?file=ir.92.pdfE. Qualcomm, How to Meet Data Demand (2011)http://www.qualcomm.com/media/documents/files/how-to-meet-data-demand-.pdfF. 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.pdfG. Qualcomm, Circuit-Switched Voice Services over HSPA (2010)http://www.qualcomm.com/documents/circuit-switched-cs-voice-services-over-hspaH. 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/21986K. Qualcomm, Performance of VoIP Services over 3GPP WCDMA Networks (2008)http://www.qualcomm.com/documents/performance-voip-services-over-3gpp-wcdma-networksL. 3GPP, TR25.903 -Technical Specification Group Radio Access Network; Continuous connectivity forpacket data users (Release 7) http://www.3gpp.org/ftp/Specs/archive/25_series/25.903/25903-700.zipM. 3GPP, TS 24.229 - IP multimedia call control protocol based on Session Initiation Protocol (SIP) andSession Description Protocol (SDP); Stage 3http://www.3gpp.org/ftp/Specs/archive/24_series/24.229/24229-930.zipN. 3GPP, TS 23.216 - Single Radio Voice Call Continuity (SRVCC); Stage 2http://www.3gpp.org/ftp/Specs/archive/23_series/23.216/23216-870.zipO. 3GPP, TS 23.237 - IP Multimedia Subsystem (IMS) Service Continuity; Stage 2http://www.3gpp.org/ftp/Specs/archive/23_series/23.237/23237-870.zip Page 21
  22. 22. P. GSMA, IR.64.20- IMS Service Centralization and Continuity Guidelineshttp://www.gsma.com/go/download/?file=ir6420.pdfQ. GSMA, IR 65.5.0 - IMS Roaming and Interworking Guidelineshttp://www.gsma.com/go/download/?file=ir6550.pdf Page 22
  23. 23. ABBREVIATIONS3GPP 3rd Generation Partnership ProjectAM Acknowledged ModeAMR Adaptive Multi-RateAMR-NB AMR NarrowbandAMR-WB AMR WidebandAPN Access Point NameBTS Base Transceiver StationCDMA Code Division Multiple AccessCPC Continuous Packet ConnectivityCS Circuit-SwitchedCSFB CS FallbackCSoHS CS Voice over HSPADCH Dedicated Transport ChannelDL DownlinkDRX Discontinuous ReceptionDTX Discontinuous TransmissionEPC Enhanced Packet CoreEPS Enhanced Packet System (i.e., LTE + EPC)E-SCC Enhanced Service Cell ChangeE-UTRAN Enhanced UMTS Radio Access Network (a/k/a LTE)F-DPCH Fractional Dedicated Physical ChannelGBR Guaranteed Bit RateGSM Global System for Mobile CommunicationsGSMA Global organization for 3GPP technologies, f/k/a GSM AssociationHS-DSCH High-Speed Downlink Shared ChannelHS-SCCH High-Speed Shared Control ChannelHSDPA High-Speed Downlink Packet AccessHSPA High-Speed Packet AccessHSUPA High-Speed Uplink Packet AccessIMS IP Multimedia SubsystemIP Internet ProtocolIPv4 IP version 4IPv6 IP version 6IR International Roaming (a GSMA document citation tool)LTE Long Term EvolutionMS Mobile StationNodeB Base Station in HSPA networksPCC Policy and Charging ControlP-CSCF Proxy - Call Session Control FunctionPDN Packet Data NetworkPDP Packet Data ProtocolPDU Packet Data UnitPRD Permanent Reference Document (a GSMA document citation tool)PS Packet-SwitchedQoS Quality of ServiceRAB Radio Access BearerRAT Radio Access TechnologyRLC Radio Link ControlRoHC Robust Header Compression Page 23
  24. 24. RRC Radio Resource ControlRTCP RTP Control ProtocolRTP Real-Time ProtocolSCC Serving Cell ChangeSIP Session Initiation ProtocolSR-VCC Single Radio Voice Call ContinuityTDMA Time Division Multiple AccessTHP Traffic Handling PriorityUDP User Datagram ProtocolUE User EquipmentUL UplinkUM Unacknowledged ModeUMTS Universal Mobile Telecommunications SystemUTRAN UMTS Terrestrial Radio Access NetworkVoHSPA 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 Page 24
  25. 25. ACKNOWLEDGEMENTSThe mission of 4G Americas is to promote, facilitate and advocate for the deployment and adoption of the3GPP family of technologies throughout the Americas. 4G Americas Board of Governor members includeAlcatel-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 BobCalaff of T-Mobile USA, as well as the contributions of Etienne Chaponniere of Qualcomm, and KarriRanta-Aho and Curt Wong of Nokia Siemens Networks, as well as representatives from the othermember companies on 4G Americas’ Board of Governors who participated in the development of thiswhite paper. Page 25

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