Deployment Aspects for VoIP Services over HSPA Networks

Transcription

1 Nash Technologies Your partner for world-class custom software solutions & consulting Deployment Aspects for VoIP Services over HSPA Networks Jens Mueckenheim, Enrico Jugl, Thomas Wagner, Michael Link, Juergen Kettschau, Monica Casado-Fernandez

2 Outline Motivation VoIP service - Voice service characteristics - VoIP overhead HSDPA scheduler aspects - Design principle - Simulation results EDCH transmission aspects - Algorithm settings - Simulation results VoIP improvements - 3GPP features for performance improvement Conclusions & Outlook Slide 2

3 Motivation From the beginning of UMTS, voice service has been efficiently transmitted as circuit switched service using the Dedicated Traffic Channel (DCH) - Advantage of spread spectrum using CDMA technology Recently, VoIP services are also considered for transmission over mobile networks - VoIP is widely used in the Internet world - With introduction of HSPA, the performance (data rate and round trip delay) of UMTS networks has been increased, which makes now VoIP viable - VoIP service allows utilizing the IMS potential, e.g. for combining with other multimedia services - The support of VoIP can be seen as a further step towards fixed mobile convergence So far, HSPA networks were mainly optimized for efficient support of volume based packet traffic such as FTP, HTTP or streaming traffic - Algorithms & settings need to be adapted to voice traffic requirements Slide 3

4 Voice Service Voice service is characterized by constant low traffic 2 ms 16 ms 2 ms talk spurt silence talk spurt voice traffic model Voice frame SID frame Overall performance is given by the total end-to-end delay - Total budget (incl. HSPA delay, transport delay, core network, etc.): 28 msec - HSPA budget: 9 msec - Overdue VoIP frames shall be discarded occurrence of frame loss Slide 4

5 VoIP Overhead VoIP itself generates relatively large overhead due to UDP/ IP - Compression is needed to meet the voice capacity requirements (RoHC) Within the transmission layer some overhead is produced in RLC/ MAC - This needs to be compensated by higher HSPA efficiency IPv4 header 2bytes UDP 12 bytes Hdr./ Pad. RLC UM 8 bit RTP 8 bytes Compr. header 12 bit 4 bytes 12 bit MAC-d PDU AMR frame 244bit AMR frame 244bit 296 bit HSPA transport block: bit Slide 5

6 HSDPA Scheduler Design The HSDPA scheduler decides at each TTI about the users to be active - Decision: which user(s) and what amount of resources (power/ code) - Usually done via ranking lists There are different options to support VoIP service - VoIP service is scheduled by modified FIFO type scheduler - Channel quality is not used for the ranking of the users - Introduction of a wait time T wait, before VoIP is ranked behind the background service - After T wait VoIP is ranked on top - Services with the same state w.r.t. T wait are scheduled with FIFO metric - Background traffic is scheduled by usually metrics considering channel quality, e.g. proportional fair - VoIP service can be also scheduled by a channel aware metric with some special rule to fullfill a minimum rate of the service Slide 6

7 Simulation Scenario Parameter # of NodeB (sites)/ sectors Pathloss model Cell radius Shadow fading Value 12 sites/ 3 sectors each (wrapped around) COST 231 Okumura Hata urban 1 m 7 db standard deviation, 1 m correlation length Mobility model Mixture: 25%AWGN + 37% PedA3 + 13% PedA3 + 13% VehA3 + 12% VehA12 BTS max. total transmit power # HS-SCCH 8 Uplink Target Load Service 1 32 W (23% reserved for common channels) 85% 12.2 k AMR speech service, 5% activity Service 2 2 MByte FTP download Slide 7

8 HSDPA Scheduler Results (I) 3 FTP Only average user throughput [kbit/sec] FIFO_ FIFO_2 FIFO_4 5 Min Rate FIFO_2/ 1FTP Voice Traffic [Erlang] VoIP Loss 9 average frame loss rate [%] 8 FIFO_ FIFO_2 7 FIFO_4 Min Rate 6 FIFO_2/ 1FTP Voice Traffic [Erlang] FIFO type schedulers provide the required QoS of VoIP traffic By adjusting the wait time T wait, a tradeoff between VoIP and background traffic can be achieved - Higher T wait, provide better throughput for the background service - Lower T wait improve frame loss performance for the VoIP service - With T wait > there is an impact of increasing background traffic onto VoIP quality Min Rate scheduler is unable to balance QoS requirements between VoIP and background traffic Slide 8

9 HSDPA Scheduler Results (II) 2 VoIP Only aggregated traffic power [Watt] aggregated traffic power [Watt] FIFO_ 6 FIFO_2 4 FIFO_4 Min Rate 2 FIFO_2/ 1FTP Voice Traffic [Erlang] FTP Only 12 FIFO_ 1 FIFO_2 FIFO_4 Min Rate 8 FIFO_2/ 1FTP In all scenarios, VoIP takes the resources from the background service Degree of resource shifting for the FIFO schedulers is adjusted by T wait - With lower T wait more resources are given to VoIP - Higher T wait keep more resources to background service - With T wait > there is an impact of increasing background traffic onto VoIP consumption Min Rate scheduler cannot efficiently balance the resources between VoIP and background traffic Voice Traffic [Erlang] Slide 9

10 EDCH Transmission Settings EDCH provides two options for data transmission - Scheduled transmission, which is esp. suited for background service - Scheduling is done on a request/ grant scheme with frequency of some 1 msec - Non-scheduled transmission, which is designed esp. for delay sensitive traffic - Fixed grant given by Radio Resource Control Outer-loop power control functionality ensures the QoS of the EDCH transmission - Parameter: target number of HARQ transmissions N target - Estimate: number of current required HARQ transmission N current - If N current < N target, transmit power can be reduced - If N current > N target, transmit power must be increased The transmission time interval (TTI) can be adjusted with different goal - 1 msec TTI allows smooth resource usage, but increases transmission delay - 2 msec TTI reduces the transmission delay, but causes more bursty resource usage Slide 1

11 EDCH Transmission Results (I) 3 FTP Only average user throughput [kbit/sec] 1.1 Tx Tx 1.5 Tx 2 ms Tx/ 1 FTP Voice Traffic [Erlang] VoIP Loss 8 7 average frame loss rate [%] 1.1 Tx Tx 1.5 Tx 5 2 ms Tx/ 1 FTP Voice Traffic [Erlang] By adjusting N target, a trade-off between VoIP and background traffic can be achieved - Higher N target, provide better throughput for the background service - Lower N target improve frame loss performance for the VoIP service - Due to the outer-loop power control there is a floor in the frame loss rate With non-scheduled transmission there is low impact of increasing background traffic onto the VoIP performance - Background traffic itself is significantly reduced 2 msec TTI has similar performance Slide 11

12 EDCH Transmission Results (II) 25 EDCH Load serving users In all scenarios, VoIP takes resources from the background service - With increased VoIP traffic less load available for scheduled transmission average cell load [%] Tx 1.3 Tx Tx 2 ms 1.3 Tx/ 1 FTP Voice Traffic [Erlang] Amount of resource is determined by N target - With lower N target more resources are given to VoIP - Higher N target keep more resources to the background service - Increased background traffic even reduces more the load available to this service 2 msec TTI has similar average resource usage Slide 12

13 Improvement of HSDPA VoIP Transmission Enhancements are mainly designed to reduce power and code consumption of the VoIP service - Fractional DPCH reduces consumption of the associated dedicated physical channels - Receive Diversity improves performance of the receiver - HS-SCCH less transmission reduces consumption for the shared control channel Most improvement is given by Rx diversity F-DPCH (1 users max) Capacity [%] UE1 256 chips UE2 UE3 UE4 UE5 UE6 1 slot = 256 chips UE7 UE8 Relative VoIP Capacity (2% frame loss, Reference: F-DPCH) UE9 UE1 - FIFO scheduler do not regard channel conditions - F-DPCH is needed to provide sufficient capacity wo RxDiv Receiver Type ADPCH FDPCH HSCCH less with RxDiv Slide 13

14 Improvement of EDCH VoIP Transmission Uplink discontinued transmission reduces the overhead of the UL- DPCCH - DTX is used when no data is sent on EDCH UL DTX Data Control Relative VoIP Capacity (2% frame loss, Reference: TTI_1) UL DTX improves esp. 2msec TTI - This mode has mostly silent EDCH transmission With enhancements, VoIP capacity can be balanced between up- and downlink Capacity [%] continuous Receiver Type UL DTX 1msec 2msec Slide 14

15 Conclusions/ Outlook VoIP service demands a special design of the transmission over HSPA - VoIP is characterized by constant low traffic and strict delay requirements - UDP/ IP overhead must be reduced to maintain voice capacity The HSDPA scheduler must be designed to handle the special VoIP characteristic - Modified FIFO seems the best way to fulfill the strict QoS of VoIP service - Application of a wait time allows to trade-off VoIP with background service The EDCH transmission must be adjusted according to the VoIP service - Non-scheduled transmission is used to meet the specific needs of VoIP - Adjustment of the target number of HARQ transmissions allows to trade-off VoIP with background service 3GPP has defined various improvements to make VoIP over HSPA more efficient - In the downlink, F-DPCH and receive diversity provide the most improvement - In the uplink, discontinued transmission is most efficient together with 2msec TTI Similar conclusions can be also drawn for VoIP over LTE - FIFO mode is favored for downlink VoIP - 3GPP has defined a semi-persistent scheduling mode, which is comparable to NST Slide 15

16 Thank you! Nash Technologies GmbH Thurn-und-Taxis-Str. 1 D-9411 Nuremberg