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Voice Over  U M T S Evolution From  W C D M A, H S P A To  L T E
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Voice Over U M T S Evolution From W C D M A, H S P A To L T E

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  • 1. Song, Peng-Peng UTRAN system engineering Voice over UMTS evolution - from WCDMA, HSPA to LTE
  • 2. Outlines
    • AMR voice characteristics
    • Voice over UMTS evolution
      • R99 DCH scheme
      • CS Voice over HSPA+
      • VoIP over LTE
    • Performance metrics
      • How fast, how big, how reliable
  • 3. AMR Voice characteristics
    • Voice telephony service: modeled as a low, fixed rate data stream.
    • AMR codec
      • AMR_NB: an “adaptive”, “multi-rate” codec that is able to adapt to variable channel conditions .
      • AMR_WB (Optional) : significant improvement for clear sound and rich voice.
    • VoIP in cellular networks
      • VoIP in IMS domain (Rel-5)
      • encapsulated in RTP/UDP protocol
      • UTRAN serves VoIP with PS conversational RAB
      • header compression is a must for wireless transmission
      • mandatory UE support
    23.85, 23.05, 19.85, 18.25, 15.85, 14.25, 12.85, 8.85, 6.6 AMR_WB multi rate (kbps) 12.2 (GSM-EFR), 10.2, 7.95, 7.4(IS-136), 6.7(PDC-EFR), 5..9, 5.15, 4.75, 1.8(SID) AMR_NB multi rate (kbps) A/D … …… voice samples compressed frame 20ms codec output voice frame RTP packet UDP packet VoIP packet UTRAN UMTS PS CN IMS application servers 40 bytes (AMR 12.2) Total voice payload on air interface 16 bits (CRC) 2 byte (RLC security) 4 byte (RTP/UDP/IP) 10 bit + padding (RTP-pre-header) protocol overhead with compressed header SID packet every 160ms during silence 15 bytes(5 bvtes + header) SID 50% voice activity factor 20 ms encoder frame length source rate 12.2kbps RTP AMR 12.2 codec Characterization Parameter
  • 4. Voice over R99 DCH
    • Support UED/UEP (unequal bit error detection and protection) against prioritized codec output sub-flows
    DCH DTCH DTCH DTCH DCCH DCCH DCCH DCCH DCH DCH DCH 3.4 kb/s DPDCH Class A bits Transport channels Physical channels Class B bits Class C bits RRC,AM NAS_DT, High prio, AM Logical channels NAS_DT, Low prio, AM RRC,UM DPCCH TFCI Transport Block Add CRC Add tailer bits Channel coding 2 nd interleaving Class A bits Class B bits Class C bits TB AMR 12.2k payload (SRB 3.4kb/s) DCCH CRC CRC 81 60 103 148 81 12 103 60 148 16 93 8 103 8 60 8 164 8 303 333 136 516 294 324 128 548 Rate matching 294 324 128 548 1 st interleaving Segmentation 1a 1b 2a 2b 3a 3b 4a 4b 4c 4d 1a 2a 3a 4a 147 147 162 162 64 64 137 137 137 137 1b 2b 3b 4b radio frame i radio frame i+1 1 2 15 510 510 CCTrCH level Phy Channel level … 1 2 15 … 6 34 510 + 90 6 34 … … … 510 + 90 Trans. ch multiplexing DPCCH DPDCH Transport Block level 1/3 Conv coding
  • 5. Voice over R99 DCH
    • AMR control: adapts AMR Codec rate to varying radio channel conditions
      • Based on radio link power: further optimizes radio resource usage
      • Based on cell load: offers a trade-off between capacity and coverage & alleviates load congestion
    6A/6B event NodeB RNC Measurement report MSC UE Tx power IuUP rate control process Transport Format Combination Control NBAP dedicated measurement process RB reconfig A complete solution accompanied by power control, dedicated measurement, adaptive rate control, soft handover while minimizing radio resource usage! cell load Transmitted code power
  • 6. CS over HSPA
    • Standardized in R7 spec - driven by NSN and Qualcomm
      • To avoid surplus “SRNS relocation” signaling between “hierarchical RNC” and “flat RNC”
    • Benefits from advanced HSPA radio interface
      • 2ms TTI -> shorter RTT
      • L1 HARQ -> improved BLER
      • delay sensitive scheduling -> guaranteed latency
    • Equivalent AMR rate control capability needed
    • UE dependency
      • “ support for CS over HSPA”
    NodeB Serving Cell Rel-7 UE PS & CS Core Network RNC CS over HSPA PS calls SRNS relocation ?!
  • 7. CS over HSPA
    • Technical implementation:
      • A new “AMR” type PDU with “CS counter” as timestamp of voice packets
      • A sequence number added in RLC header to help to determine correct order as well as detect missing packets
      • A transmission number added in MAC header to re-order packets as uplink packets experiences HARQ via E-DCH.
      • A de-jitter buffer needed on both UE and RNC
    DCH E-DCH HS-DSCH WCDMA L1 Processing HSPA L1 Processing (HARQ proc) MAC-e scheduler MAC-hs scheduler MAC-d RLC TM IuUP Proc. CS Telephony Core Network MAC-es MAC-d RLC UM PDCP (SN) (cs counter) (TN) Iub FP Iub FP NodeB RNC UE IuCS
    • Benefit: no needs of IMS core network for voice packet over HSPA
    • Capacity gain:
      • - 23% capacity gain( with 2ms HSUPA TTI) over R99 voice user numbers per cell;
      • - with CPC, will have 48% capacity gains over R99.
    A beginning for voice over “packetized” radio interface!
  • 8. VoIP over LTE
    • LTE is purely PS-domain oriented - Can LTE support voice service?
      • Yes, in term of VoIP with IMS core
      • Otherwise use “CS fallback” or “SR-VCC” feature
      • VoLGA(Voice over LTE Generic Access) underway now
    • What is the difference between circuit-switched voice and packet-switched voice?
      • NAS Layer: Call control and switching functions already have been built into CS Core network elements but in PS domain, SIP/SDP protocols are in use.
      • AS Layer: header compression mandatory for VoIP
      • AS Layer: flexible UED/UEP on “DCH-based” radio interface but not for VoIP which is based on “shared” radio interface
      • TN Layer: bearers/interfaces need to support rigid QoS & differ-Serv management for PS traffic
    shared channel
  • 9. VoIP over LTE
    • Downlink(OFDMA): dynamic scheduling (time+frequency domain) or semi-persistent scheduling
    • Uplink(DFTS-OFDM): semi-persistent scheduling
    UE 1 resource block: 180 kHz = 12 subcarriers PDCCH PDSCH Packet-switched voice over “packetized” radio interface! VoIP packets via S1 interface Multiplexing per user scheduling RLC (Segmentation, ARQ) PDCP (Header Compression, Ciphering) HARQ OFDM Signal Generation coding data modulator resource mapping eNodeB Tx to RF module time frequency Reference symbol Control channel resource User A User B User C Idle resource for data
  • 10. Performance – cell capacity in 5MHz
    • VoIP over LTE benefits from orthogonal uplink design,
    • intelligent scheduling, antenna diversity and link adaptation!
    x1 x2 x2.85 x3.78 Orthogonal uplink Intelligent scheduling antenna diversity Link adaptation
  • 11. Performance – latency Control plane latency: User plane latency: “ single-node” RAN architecture; Optimized signaling procedures 50ms 250~350ms 400~550ms dormant->connected < 100ms ~460ms >500ms idle ->connected ~100ms 2~3s >5.5s voice call setup LTE_VoIP CS over HSPA R99 AMR C-Plane latency
  • 12. Conclusion
    • Packetized radio interface can serve voice traffic pretty well when “QoS enablers” are built into each NE/interface.
      • Greater capacity by time/frequency diversity gain and multi-user diversity gain
      • Flexible channel bandwidth adjustment during one session
      • Rigid QoS and “diff-serv” management needed on each NE/interface
    shared channel
    • Market foresight:
      • CS over HSPA: controversial with new link budget & planning reqts
      • VoIP over LTE: sounds good but when will IMS enter life?
    dedicated channel
  • 13. Thanks!
  • 14. Backup - comparison of radio parameters IMS core MSC+MGW MSC+MGW CN dependency Rel-8 UE as defined in TS 36.306 Rel-7 UE that can report “support for CS voice over HSPA” in “UE Radio Capability” IE N/A UE dependency available control channel resource(PUCCH/PDCCH bandwidth) UL interference-limited UL interference-limited, DL OVSF code limited potential capacity limitation UM UM TM RLC mode Yes(RFC3095) No No Header compression No No Y DL No Y Y UL support SHO or not N/A Y Y DL N/A Y Y UL rate adjustable by UTRAN 2x2/4x2 MIMO N/A N/A DL MU-MIMO, No Tx diversity N/A N/A UL Antenna diversity dynamic or semi-persistent scheduling Enhanced PF scheduling N/A DL semi-persistent scheduling Non-scheduled mode, rate controlled by RNC N/A UL NodeB scheduling Y in case of multi-RAB N/A DL Y N/A N/A UL link adaptation(AMC) Y Y N/A DL Y Y N/A UL HARQ 1/3 Turbo(QPP interleaver) 1/3 Turbo 1/3 Conv. DL 1/3 Turbo(QPP interleaver) 1/3 Turbo 1/3 Conv. UL channel coding 1ms 2ms 10ms DL 1ms 2ms or 10ms 10ms UL radio frame PDSCH(shared PHY channel) HS-DSCH(shared PHY channel) DCH DL PUSCH(shared PHY channel) E-DCH DCH UL radio channel LTE_VoIP CS over HSPA R99 voice