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VoIP Service on HSDPA in Mixed Traffic Scenarios


									                        VoIP Service on HSDPA in Mixed Traffic Scenarios

                                                  Yong-Seok Kim
                                     Media Lab., Telecommunication R&D center
                                       Telecommunication Network Business
                                                Samsung Electronics

                                                                                                                                                                     IP Network
                                                                             UE                      NodeB               RNC                  SGSN/GGSN

   In this paper, we evaluate the capacity of voice over                          UL delay : 40ms

                                                                   UL Processing delay : 30ms                      Backhaul delay : 30ms             IP Network delay : about 42ms
internet protocol (VoIP) services on high-speed downlink                                                     NodeB-GSN:15ms, GSN-NodeB:15ms

packet access (HSDPA), in which frame-bundling is incor-           DL Processing delay : 30ms

                                                                                   DL delay : Variable
porated to reduce the effect of relatively large headers in
the IP/UDP/RTP layers. Also, the capacity of VoIP service
on HSDPA is considered in a mixed voice and best-effort                        Figure 1. End-to-end delay component
traffic scenarios. In order to guarantee QoS for VoIP ser-
vice, a design of packet scheduler based on the proportional
                                                                  DPA [5]. This is due to some inherent spectral inefficien-
fairness scheme is provided. Simulation results show that
                                                                  cies that seemingly would disappear if both voice and data
performance of VoIP service with frame-bundling scheme is
                                                                  were carried on 3G wireless radio link. Backhaul facilities
highly sensitive to delay budget. We also conclude that the
                                                                  would be more efficient because voice, data traffic and all
capacity of VoIP service on HSDPA is attractive for trans-
                                                                  signaling protocols would be carried on same IP facilities.
mission of voice, if compared to the circuit switched voice
                                                                  Hence, in this paper, it is attempted to provide system-level
and to the VoIP on WCDMA used in Release’99.
                                                                  simulation results of VoIP capacity which reflects the frame
                                                                  bundling (FB) and a best-effort (BE) service. This paper is
                                                                  organized as follows. In Section II, we present the system
1. Introduction                                                   of VoIP on HSDPA. And the simulation configuration is de-
                                                                  scribed in section III. Simulation results and conclusion are
    High-speed downlink packet access (HSDPA) system              presented in Section IV and Section V respectively.
that supports the peak rate of 14.4 Mb/s outperforms the
third generation (3G) WCDMA system specified in 3GPP
Release’99 [1]. The transmission of voice using packet            2. VoIP Service on HSDPA
data internet protocols (IPs) is arguably the hottest atten-
tion in telecommunication technology today. This is be-           2.1. Traffic model and protocols
cause it has high visibility in the consumer space. A long-
distance VoIP calling is cheaper to operate, maintain and             In this work, two traffic models are considered for the
upgrade than comparable solutions using switched digital          cases of BE service and VoIP service. In the context of
or analogue phone service. In addition, it facilitates the cre-   BE traffic, we applied the full queue traffic model assuming
ation of new services that combine voice communication            that data can be always sent when a queue of certain user
with other media and data applications such as video and          is chosen. A telephone conversation can be represented by
file sharing [2]. Early VoIP studies were focused on the           ON/OFF patterns. ON periods correspond to a conversant
wireless local area networks (WLAN) because of its con-           talking and OFF periods are due to silences. The duration
venience and achievable high-speed data rate as that of the       of both ON and OFF periods is negative exponentially dis-
wireline network [3]. Despite the success of VoIP in wire-        tributed with an average of appropriate seconds. Generally,
line and WLAN networks, the most widely held expectation          conversation traffic can be approximated to the two state
is about introducing into the latest broadband 3G technolo-       Markov traffic model with a suitable voice activity factor
gies such as CDMA2000 1X EV-DO [4] and WCDMA HS-                  [6]. The adaptive multirate (AMR) voice codec is manda-
   Table 1. Summary of end-to-end delay com-                        Table 2. Simulation parameters (HSDPA)
                                                                Parameter            Assumption
                                                                Source traffic        AMR 12.2kbps,
  Delay component                   Delay assumption            packet overheads     voice activity=0.32, 2-state Markov
  Voice encoder                     20ms(12.2Kbps)                                   Bundling(FB0-FB2)
  RTP frame bundling                FBx(20×xms)                                      ROHC 3 bytes [IETF RFC 3059]
  NodeB scheduling+HARQ             Correspond to FB            Cellular layout      Hexagonal grid, 19 sites, 3 sectors
                                    (Max.110ms if FB0)                               (NB-to-NB 1km)
  NodeB                             30ms                                             Carrier frequency 1.9GHz
  ROHC, RLC+MAC processing                                      Propagation loss     Path loss=-128.1-37.6*log(R)
  Downlink propagation                                          Shadowing model      Log Normal Std. dev. 8dB
  UE scheduling+HARQ                40ms                                             [Hata model]
  UE                                30ms                        UE speed             3km/h(50%)+120km/h(50%)
  processing,buffering,etc                                      Antenna gain         Node B 14dB / UE 0dB
  Uplink propagation                                                                 Other loss -10dB
  Backhaul delay (GSN-NodeB)        30ms                        Fading Model         Combination Ped.A(5%)
  IP network delay                  About 42ms                                       +Ped.B(45%)+Veh.B(50%)
                                                                                     Evaluated with 3GPP (TS 25.101)
                                                                UE Rx diversity      with or without considered
                                                                                     (catagory 10)
tory for voice services in WCDMA systems. During bursts         Retransmission       No RLC retransmission
of conversation, with the AMR mode of 12.2kbps, the VoIP                             HARQ (max. retrial = 6)
application generates 32-bytes voice payload at 20ms inter-     CQI delay, error     3TTI (6ms), 1%
vals [7]. During silent periods, a 7-bytes payload carries a    Scheduling           Modified PF scheduler
silence descriptor (SID) frame at 160ms intervals. A typi-      Reserved             - Common channel
cal VoIP protocol stack, which employs the real-time trans-                          power overhead 20%
port protocol (RTP), is encapsulated to the user datagram                            - Associated DCH power
protocol (UDP). This, in turn, is carried by IP. The com-                            0.3% per mobile user
bined these protocols demand a 40-bytes IPv4 header or a                             - HS-SCCH power 9dB offset
60-bytes IPv6 header. Obviously, the overhead caused from                            via associated DCH
the header to support VoIP service seriously degrades the                            - common channel code 10
spectral efficiency. Therefore, efficient and robust header                            - Associated DCH code 1
compression (ROHC) technique can be used to reduce the                               per mobile user
effect of relatively large headers in the IP/UDP/RTP lay-                            - HS-SCCH codes are considered
ers. This technique can reduce the size of the IP/UDP/RTP
headers as little as 2 or 4 bytes. Maximum compression 1
byte can be achieved by imposing limitations [8].
                                                               more packetization delay is introduced but at the same time
2.2. Frame bundling                                            overhead is more and more reduced. For conversational ser-
                                                               vices low delay is crucial, hence only few payloads are bun-
   In contrast to BE traffic, voice packets are usually very    dled. So, in this paper, the employed maximum number of
small. Hence, packing a single payload to a RTP packet data    FB is 2 (typically up to 2 in the case of AMR), represented
unit (PDU) may introduce severe overhead. For example,         by FB2. Where, FBx means that the number of adopted FB
compared to 40 bytes IPv4 header 32 bytes payload would        is x. These FB features are supported in the AMR payload
be a typical case for codec used for AMR. To decrease the      format [10].
overhead, instead of adding a single payload multiple con-
secutive payloads are packed into a single RTP PDU. Also,      2.3. End-to-end delay budget for QoS sup-
FB can be used to decrease the occurrence of bit-stuffing             port
due to the mismatch between the size of VoIP packet and
that of HSDPA media access control (MAC) frame format             To ensure end-to-end QoS in a packet-switched (PS) net-
[9]. However, there is a trade-off between delay and over-     work, the low delay is one of the most important criteria
head. That is, the more packets are bundled together the       for maintaining high-quality VoIP service. But, to attain
                                     1.0                                                                                                                  1.0

                                    0.95                                                                                                                 0.95

                                     0.9                                                                                                                  0.9
   Percentage of UEs with BLER<2%

                                                                                                                        Percentage of UEs with BLER<2%
                                    0.85                                                                                                                 0.85

                                     0.8                                                                                                                  0.8

                                    0.75                                                                                                                 0.75

                                     0.7    w/ UE Rx Diversity                                                                                            0.7           w/o FB
                                                                                                                                                                                      w/ FB1
                                    0.65                                                                                                                 0.65
                                                                                                                                                                                                          w/ FB2
                                                                 w/o UE Rx Diversity
                                                                                                      60UEs                                              0.6
                                    0.55                                                                                                                 0.55                                                  60UEs w/o UE Rx Diversity
                                                                                                      110UEs                                                                                                   100UEs w/ UE Rx Diversity
                                     0.5                                                                                                                  0.5
                                       10      20     30         40   50      60    70     80    90    100     110                                          10   20   30   40    50     60     70    80   90    100 110 120 130 140 150
                                                                 Scheduler Delay Budget [msec]                                                                                   Scheduler Delay Budget [msec]

   Figure 2. Outage versus Delay budget for dif-                                                                        Figure 3. Outage versus Delay budget for dif-
   ferent UEs w/ or w/o UE receiver diversity                                                                           ferent value of FB

high VoIP capacity, the scheduler must have sufficient time                                                           (TTI). The use of effective scheduling algorithm is neces-
to manage voice packets. Of the assumed 285ms end-to-                                                                sary for improving the throughput of system, since the HS-
end delay budget for qualified voice service, about 110ms                                                             DPA system shares resources with multi-users at the same
is available for scheduling in the downlink [11]. The delay                                                          TTI. The HSDPA system was designed for services with
in IP and backhaul network is in general bounded to 72ms                                                             high throughput for BE traffic requirements but it can also
[ref] which is fixed value allowing us to focus on the delay                                                          be used for VoIP. Generally, VoIP regarding conversational
budget within radio access network. The end-to-end delay                                                             service has the highest priority of traffic classes as it is very
budget in the case of mobile-to-mobile conversation can be                                                           sensitive to the transmission delay. The use of separate pri-
assumed as Fig. 1. Although VoIP performance depends on                                                              ority queues makes it possible to optimize HSDPA schedul-
both downlink and uplink performance, we would like to set                                                           ing for each different QoS service. This paper optimizes the
aside the consideration of both directions as comprehensive                                                          scheduling algorithm for traffics demanding different QoS
study for future research. Table 1 summarizes the assump-                                                            by using priority handling. First of all, VoIP flows must
tion of each component in terms of end-to-end delay budget                                                           be handled by higher priority than interactive traffic. Node
[12].                                                                                                                B receives the value of priority from the radio network con-
                                                                                                                     troller (RNC). Hence, we can differentiate between services
2.4. Performance criteria for VoIP                                                                                   through the priority values. Meanwhile, for VoIP service
                                                                                                                     over HSDPA, it is beneficial to include time-delay factor in
    The main objective of this paper is about the VoIP ca-                                                           scheduling algorithm. To measure delay, the scheduler puts
pacity in the sense that there exists the maximum number                                                             time-stamp in each packet as it arrives at the priority queue
of VoIP users that can be supported per sector without ex-                                                           that is operated with 8 queue buffers to support different ser-
ceeding a given outage threshold. In PS network, packets                                                             vice. Therefore, in this paper, a modified proportional fair
will be dropped under network traffic loads congestion due                                                            (PF) scheduling algorithm is adopted as follows
to packet loss and packet delay exceeding the target bud-
get. Although some packet loss occurs, the voice quality is                                                                                                       (i)        α                 (i)
                                                                                                                                                                 PMix (n) = Pr PPF (n)f (R y, Que s) ,                                     (1)
not affected if the amount of packet loss is less than out-
age threshold. To proceed with this work, we assume that                                                             where Pr is the level of priority which provides the high
the packet error rate (PER) is kept within 2%. Moreover,                                                             value to VoIP users and PPF (n) is the value of scheduling
at least 97% of VoIP users in the downlink should meet the                                                           metric of user i calculated by PF scheduling scheme for BE
above criterion [13].                                                                                                traffic. The delay function f (·) can be designed by f (·) =
                                                                                                                     (Que s)β /(R y)γ , where Que s is the size of VoIP packets
2.5. Scheduling strategy                                                                                             that must be scheduled at n-th TTI, R y is the remaining
                                                                                                                     delay budget from the current n-th TTI to the delay bound
    The MAC-hs sublayer in the Node B handles scheduling                                                             at the MAC-hs scheduler. For BE service, f (·) = 1. α, β
in the period of 2ms that is called transmission time interval                                                       and γ are appropriate weight factor for each one.
                                      1                                                                                      1.0

                                    0.95                                                                                    0.95
                                                                                                                                                                            w/ UE Rx Diversity

                                     0.9                                                                                     0.9

                                                                                           Percentage of UEs with BLER<2%
   Percentage of UEs with BLER<2%

                                    0.85                                                                                    0.85
                                                                                                                                    w/o UE Rx Diversity

                                     0.8                                                                                     0.8

                                    0.75                                                                                    0.75

                                     0.7                                                                                     0.7

                                    0.65                                                                                    0.65

                                     0.6    Scheduler Delay Budget=90ms                                                     0.6
                                            Scheduler Delay Budget=100ms                                                                                                   w/ FB0
                                            Scheduler Delay Budget=110ms                                                    0.55                                           w/ FB1
                                    0.55    Scheduler Delay Budget=120ms                                                                                                   w/ FB2
                                            Scheduler Delay Budget=130ms
                                     0.5                                                                                     0.5
                                        0                 1                    2    3                                          40         50         60    70       80     90       100          110
                                                         Number of Frame−Bundling                                                                         Number of user

   Figure 4. Outage versus Number of FB for dif-                                           Figure 5. Outage versus Number of user for
   ferent scheduler delay budget                                                           different value of FB

                                                                                        missions, and the combined signal has higher probability
3. System-Level Simulation Configuration                                                 of being successfully decoded. Finally, it has to be men-
                                                                                        tioned that we simulate 100,000 TTI snapshots in average
    To investigate the capacity of VoIP service over HSDPA                              for investigating the performance of the system. The main
system with a mixed voice and BE traffic, a system-level                                 simulation parameters are summarized in Table 2.
computer simulation is accomplished in this paper. The
simulations are carried out with a regular hexagonal 19 cel-                            4. Simulation Results
lular model, where the distance between Node B is 1km.
Mobile terminals should be uniformly distributed on the 19-
cell layout for each simulation run and assigned different                                 In this section we evaluate the capacity of VoIP with the
channel models according to the channel model assignment                                effect of FB and BE traffic in the combination of various
probability specified in [14]. Note that a realistic model of                            fading channel environments (Ped.A 5% + Ped.B 45% +
the wave propagation plays an important role for the signif-                            Veh.B 50%). As before described, capacity is defined as
icance of the simulation results. Shadowing is modelled by                              the number of UEs satisfying above outage condition of all
a log-normal fading of the total received power and a ba-                               UEs, this is more than 97%. If an UE’s combined PER is
sic attenuation is determined by the Hata model. Moreover,                              more than 2%, the user is considered in outage. The various
we reserved the resources for control and common channel                                results are investigated by specific performance parameters
overhead factors such as OVSF codes and HSDPA power                                     such as the percentage of UEs satisfying outage limitation
to obtain the provided simulation results. As mentioned                                 and the sector throughput.
above, we applied the RTP/UDP/IP packet header compres-
sion using IETF RFC 3059 where the total size of all com-                               4.1. The effects of FB on the capacity of
pressed header is with 3 bytes (1byte ROHC base header                                       VoIP service over HSDPA
+ 2bytes UDP checksum). Further, the fast link adapta-
tion and hybrid ARQ (HARQ) modules are employed in                                         The effects of FB on the capacity of VoIP service without
this work for throughput enhancement. While traditional                                 considering for BE service are investigated in Fig. 2, Fig. 3,
WCDMA systems use power control to mitigate channel                                     Fig. 4 and Fig. 5. Fig. 2 shows the outage performance as a
fading, HSDPA employs rate control based link adaptation                                function of scheduler delay budget for different number of
where Node B transmits at full power and adjusts modu-                                  user when there is no FB (FB0), with or without UE receiver
lation and coding sets (MCS) according to channel varia-                                diversity. Here, UE receiver diversity means that the po-
tions, maximizing instantaneous usage of the wireless chan-                             tential of achieving maximum-ratio combining (MRC) gain
nel. HARQ scheme is also introduced to recover transmis-                                from the 2 receiver antenna in the UE-site. From the figure,
sion failures. When mobile detects a transmission failure, it                           we observe that the employment of UE Rx diversity result
sends a request to Node B for retransmission. Mobile com-                               in the additional capacity over the corresponding UE with
bines soft signals of both original and subsequent retrans-                             single antenna system. This is because the

   Percentage of VoIP UEs with BLER<2%


                                                                                                                                             Total Throughput [Mbps]


                                         0.4                                                                                                                           1.5

                                           0                                                                                                                                      90                                                                                   80
                                         110                                                                                                                                 Sc        80                                                                         70
                                            100                                                                                                                                hed       70                                                                  60
                                                   90                                                                                                                              ule        60                                                       50
                                                       80                                                                            80                                                rd         50                                          40
                                               Sc                                                                               70                                                        ela         40                             30
                                                  hed       70                                                                                                                                yb
                                                      ule                                                                  60                                                                    ud        30                   20                     UEs
                                                          r d 60 50                                              50                                                                                 get        20          10                 f VoIP
                                                             ela                                          40                                                                                            [m        10                   be o
                                                                 yb     40                           30                                                                                                    sec         0         Num
                                                                       get 30 20              20                     UEs                                                                                       ]
                                                                                         10               f   VoIP
                                                                            sec 10                    be o
                                                                                     0             Num

                                                                                                                                             Figure 7. Total throughput versus Delay bud-
   Figure 6. Outage versus Delay budget and                                                                                                  get and number of VoIP users
   number of VoIP users

                                                                                                                                             Table 4. Capacity of VoIP without FB in a
   Table 3. Capacity of VoIP with FB in a single                                                                                             mixed traffic scenario
   traffic scenario

     Capacity                                                              Ped.A Ped.B Veh.B Comb.                                                                                                                     Voice Capacity T-put[kbps]
 w/o UE Rx FB0                                                               60       85      80    80                                     WCDMA                                     AMR(CS)                                 66            406
  Diversity   FB1                                                            40       80      80    75                                     (Rel.’99)                                  VoIP(PS)                               54            410
              FB2                                                            25       70      55    55                                      HSDPA                                    Only VoIP                               80            395
 w/ UE Rx FB0                                                               135      130     110   110                                                                                 Mixed                                 65            589
  Diversity   FB1                                                           125      125     105   105                                                                                Only BE                                 -           1602
              FB2                                                           120      115      95    95                                                                            Remark                                   w/o UE Rx diversity
      Remark                                                                66 : CS Capacity on WCDMA
                                                                                54 : VoIP on WCDMA

                                                                                                                                          than 110ms when FB0 [9]. In summary, these results have
                                                                                                                                          shown that the FB can be employed in VoIP service by giv-
probability of success for the initial transmission of VoIP                                                                               ing larger scheduler delay budget since reduction of voice
packet becomes more increase. In Fig. 3, we evaluate                                                                                      packet transmission delay can fully compensate the FB de-
the effect of FB on outage performance, when the num-                                                                                     lay. Fig. 4 characterizes the effect of FB on outage perfor-
ber of users is 60 in case of UE single antenna and 100                                                                                   mance as a function of the number of FB when the number
with receiver diversity. According to the results, the voice                                                                              of user is 60 in case of UE single antenna. We note from
transmission with FB has a higher sensitivity to the delay                                                                                the figure that the outage performance is little degraded as
budget in the scheduler. Especially, it is more intensive in                                                                              a RF scheduler delay budget increases. Fig. 5 characterizes
constraint of small delay latency, since FB increases VoIP                                                                                the outage performance as a function of the number of users
packet arrival interval and packet size. For example, when                                                                                when FB=0, 1, and 2. Here, 90ms maximum delay budget
aiming for an identical percentage value of 0.9, in case of                                                                               is assumed. We note from the figure that for FB=1, the out-
100 UEs, required delay latency to achieve outage is 35ms,                                                                                age performance is little degraded as the number of users
65ms, and 100ms for FB0, FB1, and FB2, respectively. This                                                                                 increases. By contrast, for FB=2, it did a great deal of per-
imply that the VoIP capacity may be reduced if the FB is in-                                                                              formance degradation to outage. Table 3 summarizes the
cluded, due to the insufficiency of delay budget in RF sched-                                                                              capacity of VoIP with FB or without FB in various prop-
uler (110ms when FB0, 90ms when FB1, 70ms when FB2).                                                                                      agation conditions for multi-path fading environments for
However, note that the VoIP capacity may not be reduced                                                                                   HSDPA. The results confirm that VoIP service over HS-
although the FB is employed, if the available delay budget                                                                                DPA without FB provides significantly higher capacity if
in RF scheduler is larger                                                                                                                 compared to both VoIP and circuit-switched voice traffic on
WCDMA (Release’99) [1], [5].                                   References

                                                               [1] H. Holma and A. Toskala, WCDMA for UMTS, John
4.2. The capacity of VoIP service in a mixed                       Wiley and Sons, Third Edition, 2004
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                                                               [2] B. Douskalis, IP Telephone, Englewood Cliffs, NJ:
                                                                   Prentice-Hall, 2000
    Fig. 6 and Fig. 7 present the capacity of VoIP service     [3] W. Wang, S.C. Liew and Victor O.K. Li, ”Solutions to
without considering for FB in a mixed voice and best-effort        Performance Problems in VoIP Over a 802.11 Wireless
traffic scenario, where UE receiver diversity does not in-          LAN,” IEEE Trans. Veh. Technol., vol.54, no.1, pp.366-
cluded. Fig. 6 shows the outage performance as a function          384, January 2005
of scheduler delay budget and the number of VoIP users
in the combination channel environments. We observe that       [4] Q. Bi, P.C. Chen, Y. Yang and Q. Zhang, ”An Analysis
VoIP service can be supported with satisfying the outage           of VoIP Service Using 1xEV-DO Revision A System,”
limitation if the delay budget of scheduler and the number         IEEE JSAC, vol.24, no.1, pp.36-45, January 2006
of VoIP users are suitable. For example, when aiming for
an outage percentage value of 0.97 that is the outage lim-     [5] B. Wang, K.I. Pedersen, T.E. Kolding and P.E. Mo-
itation to provide VoIP service, in the case of scheduler          gensen, ”Performance of VoIP on HSDPA,” IEEE Proc.
delay budget, the required delay to achieve outage is over         VTC 2005, Spring, 2005
60ms. And in the case of the number of VoIP UE, the max-       [6] 3GPP TR 25.896, Feasibility Study for Enhanced Up-
imum capacity user to provide voice service is below 65.           link for UTRA FDD
In Fig. 7, the effects of VoIP service on total throughput
for the mixed traffic scenarios are evaluated, when the num-    [7] 3GPP TS26.236, Packet switched conversational multi-
ber of BE traffic UEs is 40. According to the results, we           media application; Transport protocols
note that the increase of the number of VoIP users exhibits
throughput worsen remarkably. This is because VoIP users       [8] IETF RFC 3059, Attribute List Extension for the Ser-
occupy an overwhelming majority in the given scheduling            vice Location Protocol, February 2001
times to transmit packets by scheduler’s priority strategy.    [9] G. Rittenhouse and H. Zheng, ”Providing VoIP Ser-
Finally, table 4 summarizes the capacity of VoIP and the           vice in UMTS-HSDPA with Frame Aggregation,” Proc.
total throughput on HSDPA in combination channel condi-            ICASSP, 2005
tions. VoIP service in mixed conditions has a lower user
capacity than VoIP only service, although VoIP user is ser-    [10] IETF RFC 4352, RTP Payload Format for the Ex-
viced with higher priority by scheduling strategy. This is         tended Adaptive Multi-Rate Wideband (AMR-WB+)
due to the reserved resources for control and common chan-         Audio Codec, January 2006
nel for BE traffic users on HSDPA.
                                                               [11] ITU-T G.114, Transmission systems and media - Gen-
                                                                   eral characteristics of international telephone connec-
                                                                   tions and international telephone circuits
5. Conclusion
                                                               [12] 3GPP TR 25.853, Delay Budget within the Access
    We have examined the system capacity of VoIP service
                                                               [13] 3GPP2 TSG-C.R1002-0, CDMA2000 Evaluation
on HSDPA considering in the context of FB and BE traffic
                                                                   Methodology, version 1.0, 2004
service. Our simulation results show that the capacity of
VoIP traffic is reduced because of FB and BE traffic service,    [14] 3GPP TS25.101, User Equipment radio transmission
and the throughput of BE traffic is decreased as VoIP service       and reception (FDD)
is taken into account. from the viewpoint of FB, the FB
can be employed in VoIP service by giving larger scheduler
delay budget since reduction of voice packet transmission
delay can fully compensate the FB delay. However, HSDPA
is attractive for provision of VoIP service as compared to
WCDMA (Release’99) if FB is limited in number according
to the scheduler delay budget in a mixed voice and best-
effort traffic scenarios.

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