The Performance Comparison between WiBro and

HSDPA

Simon Shin, Chan-koo Kang, Joung-Cheol Kim, and Se-Hyun OhNetwork Engineering Development Team

Network R&D Center, SK Telecom11, Euljiro2-ga, Jung-gu, Seoul 100-999, Korea

petites flammesinate.com

Abstract-We evaluated and compared the performance ofWiBroand HSDPA, which are the most competitive systems for high datarate mobile service. WiBro is the new Korean standard forwireless and broadband portable Internet. Evaluation was doneby cell-planning tool, link, and system level simulation. HSDPAshowed the inferior performance in multipath fading channel,while WiBro did nearly good performance. WiBro provideshigher data rate transmission in multipath fading channel due toOFDMA and cyclic prefix. HSDPA was more robust in Dopplershift fading because of its shorter TTI. WiBro provides betteroverall performance in air-link comparing with HSDPA. HSDPAperformance degradation in multipath channel is similar withexperimental results in lxEV-DO.

Keywords-HSDPA, WiBro, IEEE 802.16e, and OFDMA,Capacity

I. INTRODUCTIONThe growing demands for advanced mobile multimedia let

the wireless mobile Intemet access be developed rapidly.Wireless mobile Intemet access is becoming an importantsegment for the wireless industry. The new system named'WiBro' is proposed in Korea and is being standardized. WiBromeans wireless broadband Intemet. It is to provide wirelessIntemet access with PSS (Portable Subscriber Station) under thestationary and medium-speed mobile environment. WiBro isstandardized by Telecommunications Technology Association(TTA). WiBro is compatible with IEEE 802.16e, which is theextension to 802.16d/a physical and MAC layer for mobileaccess. Its frequency bands are 2>6 GHz and channel bandwidthis less than 5 MHz. It supports the low mobility in non Line OfSight(LOS) circumstances. IEEE 802.16e standardizationstarted in November, 2003 and physical layer standardization isalmost completed in April, 2005. WiBro was assigned the 2.3GHz band and 10 MHz bandwidth in Korea.

WiBro service should provide seamless connectivityregardless of the place and time. Service shall support thevarious types of wireless multimedia applications and thevarious types of multimedia-enabled terminals such as handset,notebook, PDA, or smart phone. Service consists of threeclasses: real-time service, non-real time service, and best-effortservice. Real-time service imposes delay constraints whilerequiring the guaranteed resource allocation during the sessionsuch as audio/video streaming and interactive game. Non-realtime service does not impose any delay constraints while

requiring the guaranteed resource allocation during the sessionsuch as ftp and e-commerce. Best-effort service does not imposeany delay constraints while requiring no guaranteed resourceallocation the given service such as web browsing and e-mail [1][2].

There is another advanced technology for high data ratemobile communication. HSDPA is the most remarkable andcompetitive systems for third generation(3G) service. HSDPA isthe abbreviation of High Speed Downlink Packet Access andRelease Five of WCDMA. It is standardized by 3GPP forevolution ofWCDMA. It reuses theWCDMA Node-B, which iscommercially being operated. Therefore it can be economicallyinstalled and enables the fair price. HSDPA also has thebackward compatibility with existing WCDMA system andhandset. HSDPA is popular in network operators such as SKTelecom and NTT Docomo because they already invested theWCDMA networks.

Both WiBro and HSDPA are developed for mobile dataservice. HSDPA and WiBro will severely compete with eachother for the next generation mobile communication marketbecause both of them will be commercialized next year. Twosystems can serve the portable Intemet with data rate of severalMbps. They have the similar capacity and coverage.Nevertheless, they have different physical layer and networkstructure and this induces the performance difference. We willreview the physical layer characteristics of two systems andanalysis how their difference aspects the performance in variouschannel condition. We will also compare the strong and weakpoints based on the link and system level simulation.

II. PHYSICAL LAYER OF WIBRO AND HSDPABoth WiBro and HSDPA use the 10 MHz bandwidth,

H-ARQ(hybrid auto repeat request), AMC (adaptablemodulation and coding), and turbo coding for channel coding.HSDPA uses the QPSK and 16QAM for MCS. WiBro uses theQPSK, 16QAM, and 64QAM. Highest data rate of WiBro isfaster than that ofHSDPA because of 64QAM. HSDPA adoptsthe Frequency Division Duplex(FDD) and CDMA whereasWiBro does the Time Division Duplex(TDD) and OFDMA.OFDMA enables the robustness for multipath fading by usingcyclic prefix(CP). Advanced RAKE receiver of CDMA alsoprovides the robust performance in the multipath condition [3].This technology is not adopted because of complex

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TABLE 1. WiBRo SYSTEM PARAMETERSsubcarriers and 42 symbols per one frame. One frame isWiBro's TTI and its length is 5 ms. 27 and 15 symbols are usedfor downlink and uplink, respectively. Three symbols for bothdownlink and uplink are used for control and signaling. 24 and12 symbols are used for downlink and uplink traffictransmission, respectively. Data rate decision process ofWiBrois similar with it ofHSDPA despite channel structure difference.Portable Station Subscriber(PSS, handset) selects the CQI frommeasuring CINR and PER. Radio Access System(RAS, basestation) decides the MCS by receiving CQI from PSS every 5ms. PSS and RAS is the equipment having same function withUE and Node B, respectively. Specification of WiBro issummarized in Table I. Fig. 1 shows the frame structure. The bigdifferences between WiBro and E[EE 802.16e are the structureand performance of preamble, sub-carrier permutation inFCH/DL MAP, the existence of idle mode/paging, and so oneven though WiBro is compatible with IEEE 802.16e[4], [5].

Il.0,

- * ___ _ _ _

_ _ _;;_- - _ T C_xB nd Selectlon Ut r,mntrol alverssity Bonl selisctlon

Figure 1. Frame Structure

implementation. WiBro set CP 14.4 us which means thatmultipath of 4.32 km is allowable. TDD enables asymmetricradio resource assignment on downlink and uplink. WiBro uses2:1 ratio for downlink and uplink transmission. Effectivebandwidth of downlink and uplink is 6 MHz and 3 MHz,respectively, whereas both of downlink and uplink uses 5 MHzin HSDPA.

HSDPA is WCDMA release five and provides high data rateservice on downlink. HSDPA uses the High Speed PacketDownlink Shared Channel(HS-PDSCH) for high data rateservice. HSDPA provides the flexible high data rate service byAdaptable Modulation and Coding(AMC), while WCDMAuses fixed modulation and coding scheme. User Equipment(UE,handset) selects the channel quality indicator(CQI) frommeasuring CINR and Packet Error Rate(PER). Node B(basestation) decides the modulation and coding scheme(MCS) byreceiving CQI from UE every 2 ms. That is to say, HSDPA'sTTIis2ms.

Channel structure ofWiBro is totally different with HSDPAbecause it is not based on CDMA but OFDMA. WiBro has 846

III. PERFORMANCE COMPARISON BETWEEN HSDPA ANDWIBRo

A. Coverage ComparisonService coverage is determined by various factors. They are

CINR, geometry, path loss, and so on. Geometry is the in-celland other-cell power ratio and shows how much cell isoverlapped. The geometry is infinite in a single cell conditionand 1/3 is center position among three cells. Path loss isdominant factor of coverage in the single cell, but the geometryis more important factor in the multi-cell condition. The receiversensitivity is as follows in multi-cell condition, while it is therequired CINR addition to thermal noise in single cell.

S = CINR * I

= CINR * (NoWNf+1/G * S)

= CINR * (1 - I/G * CINR) * NoWNf (1)S is receiver sensitivity, CINR is required signal to

interference ratio, I is the sum of thermal noise and other-cellinterference, and G is geometry. Fig. 2. shows the Rx sensitivityincrease by other-cell interference.

Figure 2. /G vs. Rx sensitivity

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System Parameters ValueSampling Frequency 10 MHzNumber of used tones 864 out of 1,024Number of pilot tones 96OFDMA symbol time 115.2 lis

Ratio of cyclic prefix to the OFDM symbol 1/8Number of symbols in a frame 42

TrG+RTG 161.6 pisNumber oftones per bin (DLWUL) 9(8 data+] pilot tones)Number oftones per tile(UL) 9(8 data+1 pilot tones)

Number of bins per AMC sub-channel(DL/UL) 6Number oftones per diversity sub-channel(DL) 48 data tonesNumber of tiles per diversity sub-channel(UL) 6

-512 kbps- 1024 kbps

_ -86-

-91-

- -96'

r -1060 0.5 1 1.5 2 2.5

1/G (other-cel to h-cell)

8

IXT44=0 cii.20 Qz.m [J_Lj.as R.T41i.29.

Figure 3. Capacity Simulation Process

Eq.(1) shows the broadband system needs higher sensitivitybecause ofhigher thermal noise. WiBro uses the 8.3 MHz signalbandwidth, while HSDPA uses 3.84 MHz. Thermal noise ofWiBro is 3.4 dB bigger than that of HSDPA. 3.4 dB results inthe 19 % coverage shrink. Real coverage is determined byrequired CINR, and it is severely different with channelcondition.

B. Capacity ComparisonSystem capacity is determined by CINR distribution,

scheduling algorithm, and link-level performance. Fig. 3.explains the capacity simulation process. The CINR distributionis given by inter-cell interference. We simulated it byCelIPLANO. CelIPLAN® is the cell planning tool thatsimulates the path loss and CINR considering terrestrial andresidential environment in multi-cell condition. Fig 4. is one ofthe CellPLAN® result which shows the Rx power distributionoftarget Node B or RAS. Fig. 5. is the CDF ofgeometry derivedfrom CelPLAN® results. The average CINR per a sub-channelis expressed as (2) in WiBro network.

where,

CINR= IEIEPcLpGbGfK k=a]. l= I +NoW

l PCLjG.Gf,6,jj=i

Pc: power per a carrierK : a number of sub - channel allocated int o a cella: a number of sub - carrier allocated into a sub - channelLp: radio propagation lossloc : interference from the other cellsNo: thermal noise densityW: sytem bandwidthGb: BTS Antenna Gain including cable lossGf: fade margin including shadowing

(2)

0.980.92

0.88

0.84

0.81 1.5 2 2.5

othercellpower/ h-cellpower

Figure 5. PDF ofGeometry

J: a number of other cell, 18

Lj: radio propagation loss between target cell and other cell

1: when ith sub -carrier of k channel in target cell

,qk = J is allocated in j cell

10: else I

HSDPA SIR calculation is more complicated because of itschannel structure. SIR ofHSDPA is calculated as follows:

P I,Erir21-1 = I.b t i=

(tIK)." = --

P..

G_, (UE) =

Ellrr (G_,,2G + E IIrkI')j=l s1t1* (3)

p. gn(UE)xguEUE,n SHUE,.

_-., .f- - IrrT x Y..p_i. + vL,. 11," 11'xP.~gPk XUSH)XUE (noisek=l,*n1t ll PLUE,k X SHUE,k (4)

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Figure 6. Simualtion Flow ofMAXIM

|-HSDPA NW Bro

4

3

0Ped A 3km/h Ped B lOkm/h Veh A 60kmrAi

channelmodel

Figure 7. Downlink Capacity

ISHSDPA WiBro

a. 0Ped A 3km/dh Ped B 10kmi/h Veh A 60krm/h

channel model

Figure 8. Frequency Efficiency in Round Robin Scheduling

Y complex amplitude of i,,, pathG,, geometryfactorJ Number ofmultipathN Number of interfering sectorg,L single path complex amplitude ofinterfering sector k

g, (UE) antenna gain ofserving sector ngUE antenna gain ofuser equipmentP- thermal noise ofUE

PL]v., Path loss between UE and interfering sector k

where, SH,,tshadowing loss between UEand interfering sector k

CQI by Given CINR was calculated by link levelsimulation(LLS)[6]. The LLS ofHSDPA was simulated by SKTelecom and KAIST. We used the LLS result of "2.3 GHzportable Internet proposed standard technology evaluation" forWiBro. The LLS was done by Samsung Electronics and ETRI.We simulated the link level performance in six kinds of channelcondition - Rayleigh, pedestrian A 3 km/h, pedestrian B 3 km/h,and vehicular A 30, 60, and 120 km/h. After LLS, we calculatedthe sector capacity through system level simulation(SLS). Weused the Multimedia Access System-level SlMulator(MAXIM)for SLS. MAXIM is co-developed with Korea University.MAXIM simulates the sector capacity using traffic modelingand scheduling in multi-user condition. SLS flow is as followsin Fig. 6. In Fig. 5 A and B is same if there is no frame error. Aand B is practically different because there is frame error. B iscalculated from A through H-ARQ process. Schedulingalgorithm determines the user served on this time and there areround robin, proportional fair, and Max CINR. Link-levelperformance shows the possible data rate in given CINR andchannel condition. When we use the Round-Robin scheduler inSeoul CINR distribution, downlink sector capacity is shown asFig 7.

Sector throughput comparison is not fair for the downlinkand uplink bandwidth of WiBro is asymmetric. TDD is one ofthe reasons ofWiBro's superior capacity. WiBro assigns 2/3 of9 MHz on the downlink. Therefore WiBro can use morebandwidth than HSDPA for downlink service. Therefore wecompare WiBro and HSDPA throughput per frequency unit. Fig.8 shows the frequency efficiency that is calculated from thesector throughput divided by downlink bandwidth. WiBro andHSDPA performance is similar in pedestrian A channel,whereas HSDPA performance is severely degraded inpedestrian B and vehicular A channel. WiBro is also moreefficient than HSDPA in pedestrian A, because pedestrian Amodel also has the multipath. WiBro performance is still good insevere multipath channel as like pedestrian B and vehicular Abecause the CP prevents Inter Symbol Interference(ISI) beoccurred. HSDPA shows poor performance in multipathchannel because RAKE is not effective in spread factor 16 andQAM scheme. WiBro is more adequate than HSDPA in a denseurban area. Fig. 8 shows the WiBro and HSDPA's FrequencyEfficiency.

We can experimentally confirm the RAKE performance inmultipath channel using lxEV-DO system. We measured thedata rate in one and three path channel condition and observedthe 40 % capacity shrink in the three-path channel. It is a similarresult to HSDPA simulation. Fig. 9 shows the IxEV-DO sectorthroughput in one and three path channel. This experimentalresults are coincident with Qualcomm's simulation results[7].

These simulations do not include retransmission by frameerror. I % of frame transmission is statistically failure becauseLLS results was obtained assuming I % FER. Failed frame isretransmitted if frame error is occurred. Both WiBro andHSDPA use the H-ARQ. H-ARQ reduces the throughputdegradation by frame error. Fig. 10 shows the performancedegradation by frame error whether H-ARQ is adopted or not.

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[4] TTA, TTAS.KO-06.0064, Specifications for 2.3 GHz band PortableInternet Service-Physical Layer.

1 path 3km h lpath 120km /h 3path 3km /h [5] TTA, TTAS.KO-06.0065, Specifications for 2.3 GHz band PortableInternet Service-Medium Access Control Layer

1.2 [6] Junsu Kim, Sung Ho Moon, and Dan Keun Sung, "Multi-QoS Scheduling_0 - Algorithm For Class Fairness in High Speed Downlink Packet Access,"- 0.8 PIMRC 2005, Berlin, Gerrnany(D o .6 r > # ^$[7] Peter J. Black and Mehmet I. Gurelli, "Capacity Simulation ofcdma2000

t@0.4 9 __-- ~ 1 0 IxEV Wireless Internet Access System", MWCN 2001, Recife, Brazil

-106 -102 -98 -94 -90 -86 -82Rx power [dBm I

Figure 9. 1 xEV-DO performance

* HSDPA - - -WBro

100

0w/oFER H-ARQ w/oH-ARO

channe m ode

Figure 10. performance degradation by Frame error

Performance degradation ofHSDPA is less than WiBro. TTI ofHSDPA is 2 ms which is shorter than 5 ms, TTI of WiBro. IfTTI is long, CQI mismatch probability is high because ofdynamic channel variation.

IV. CONCLUSIONWe compared the air-link performance of WiBro and

HSDPA. For the capacity, WiBro shows better performancethan HSDPA owing to its robustness in the multi-path fadingchannel. HSDPA also has a good performance in AWGN andRayleigh channel, but RAKE performance is deeplydeteriorated in multi-path fading channel. Multi-pathdegradation of HSDPA system was similar with IxEV-DOsimulation and experimental results. HSDPA TTI is shorter thanWiBro TTI and this makes HSDPA to be robust to the dynamicchannel variation. Overall performance ofHSDPA is inferior toWiBro even though HSDPA has less CQI mismatching.Nevertheless HSDPA is very attractive to mobilecommunication industry because it uses the establishedWCDMA network.

REFERENCES

[1] 3GPP, Technical Specification TS22.105, V.4.0.0, Services and ServiceCapabilies.

[2] Jaana Laiho, Achim Wacker, and Tomas Novosad, Radio NetworkPalnning and Optimisation for UMTS, John Wiley & Sons, 2002,pp.365-410

[3] G. E. Bottomley, T. Ottosson, and Y.-P. E. Wang, "A Generalized RAKEReceiver for Interference Suppression" JSAC., vol. 18, 2000

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