VOICE AND DATA PERFORMANCE OF THE cdma2000 1XEV-DV SYSTEM

Transcription

1 VOICE AND DATA PERFORMANCE OF THE cdma2000 1XEV-DV SYSTEM R. Thomas Derryerry, Ln Ma, Zhgang Rong 1 Noka Research Center 6000 Connecton Drve MS 2:700 Irvng, Texas USA ABSTRACT The antcpated ncrease n future mole wreless packet data servces has challenged the current Thrd Generaton (3G) standardzaton odes to respond wth evolved 3G system specfcatons capale of provdng ncreased data throughput. The cdma2000 specfcaton has undergone a recent evoluton (1XEV-DV) wth the goal of mprovng data throughput whle smultaneously provdng coexstng voce servces wthn the same rado frequency (RF) carrer [1]. Ths paper descres the forward and reverse lnk enhancements resultng n cdma2000 Revson C and presents system level performance data under mxed voce and data scenaros. 1. INTRODUCTION The general oectve regardng end-user servces durng the development and standardzaton of the current 2G networks (e.g. IS-95) was to match the servces provded y PSTN and ISDN;.e., the target was to create a mole telephony network, whch delvers pre-defned earer servces and teleservces whle eng oth spectrum effcent and economcally attractve [1]. In short, the goal of 2G was to delver mole low rate crcut swtched voce and low rate data. The next goal for the cellular ndustry was to ntroduce connectvty to packet data networks va cellular systems whle ncreasng voce capacty. Ths was largely accomplshed wth the thrd generaton (3G) evoluton of IS-95 to cdma2000. From the outset of defnng 3G systems, there were clear goals not only to ncrease the gross t rate over the rado, ut also to mprove packet-swtched earer servces y ntroducng support for varous QoS classes. Furthermore, the users alty to communcate over a packet-swtched earer servce whle smultaneously engaged n a voce call (or other teleservces) was deemed to e very mportant. Recent trends n the Mole IP and ndustry trends ndcate oth a stronger demand for packet data servces and capacty. To satsfy ths antcpated ncrease n packet data, t s mportant to ncrease the data throughput of 3G systems whle smultaneously provdng the needed voce servces over the same RF carrer snce a sgnfcant porton of a wreless operator s revenues are currently derved from voce servces. 1XEV-DV (also known as cdma2000 Revson C) accomplshed ths task. Ths feature of 1XEV-DV allows the wreless operators to utlze ther spectrum more effcently and provdes a means to alance the voce and data load n ther system ased on ther specfc needs. 2. 1XEV-DV OVERVIEW 1XEV-DV s an enhancement to cdma2000 s data carryng capalty targeted at provdng hgher rates on the forward lnk. The 1XEV-DV system was desgned to mantan ackwards compatlty to all prevous versons of IS-95 and cdma2000 ncludng the exstng channels and sgnalng structure. An equally mportant feature of 1XEV-DV s that t does not requre new ase statons,.e. the coverage footprnt s retaned. The enhancements occur at the physcal layer of the specfcaton and are controlled y the upper layers. For the purposes of ths paper, only the physcal layer enhancements wll e summarzed. 2.1 Forward Lnk Enhancements 1XEV-DV ncorporates several new features ult around ts tme dvson and code dvson multplexng (TDM/CDM) capalty. The data earng traffc channel s referred to as the Forward Packet Data Channel (F-PDCH or PDCH). The PDCH s shared y the packet data users and can not undergo soft handoff (SHO). Dependng upon system loadng the PDCH conssts of 1 to 28 code-dvson-multplexed quadrature Walsh suchannels, each spread y 32-ary Walsh functon. It can transmt any of a set of fxed packet szes of 408, 792, 1560, 2328, 3096, and 3864 ts. The system has varale packet duratons of 1.25, 2.5, and 5 ms. The system also employs channel-senstve schedulng va adaptve modulaton and encodng wth hgher order modulaton of QPSK, 8PSK, and 16QAM. The system makes use of a concatenaton of Forward Error Correcton (FEC) codng and an Automatc Repeat request (ARQ) protocol known as Hyrd ARQ (HARQ). HARQ operatng at the physcal layer facltates shorter roundtrp delays as compared to those assocated wth hgher-layer retransmsson schemes employed n the Rado Lnk Protocol (RLP). Ths mportant attrute of 1XEV-DV reduces the proalty of a data sesson tmeout (e.g. TCP/IP) as compared to RLP retransmsson delays. The system has varale code dvson multplexed common control channels of 1.25, 2.5, and 5 ms wth a asc user packet schedulng granularty of 1.25 ms. The control channel carryng the user s MAC ID, Encoder packet sze, HARQ control nformaton, and roadcast of avalale Walsh codes s referred to as the Forward Packet Data Control Channel (F-PDCCH or PDCCH). The system may use up to two PDCCHs to enale data-earng servces to two dfferent users 1 Sumtted to Internatonal Communcaton Conference 2003 (ICC 2003)

2 smultaneously. Approprate reverse lnk enhancements necessary to support forward lnk operaton of 1XEV-DV were made as well. 2.2 Reverse Lnk Enhancements As many of the servces n the near future are expected to e forward lnk ntensve, the maorty of the effort n desgnng 1XEV-DV focused on enhancng the forward lnk. A susequent release wll enhance the data earng capalty on the reverse lnk. Wth ths n mnd, only mnor addtons were made to the reverse lnk so as to support the enhanced forward lnk. To support HARQ functonalty, the Reverse Acknowledgment Channel (R-ACKCH) was added to provde synchronous acknowledgements to the receved forward lnk data packet transmssons. The Reverse Channel Qualty Indcator Channel (R-CQICH) s used y the mole staton to ndcate to the ase staton the channel qualty measurements of the est servng sector. The mole staton selects the est servng sector y applyng a Walsh cover correspondng to the selected servng sector. In determnng the 1XEV-DV desgn, a sgnfcant effort was undertaken to evaluate the system performance wth mxed data and voce servces. 3. SIMULATION METHODOLOGY The smulaton methodology used n system smulaton follows the requrements of the evaluaton methodology [3]. Lnk level smulatons are performed to determne the energy requrement to acheve target Packet Error Rate (PER) for a sngle rado lnk [4]. System level smulatons are then performed usng the lnk level results as a look-up tale to calculate the system performance parameters ncludng capacty, data throughput, outage level. 3.1 Modelng of Packet Data Channels For each tme nterval, the ase staton decdes the transmsson format for the scheduled users. The transmsson format ncludes encoder packet sze, slot duraton and numer of Walsh codes that may e used. At the recever sde, the mole staton (MS) calculates the sgnal to nterference rato (SIR) and then decdes f the packet s erased or not Transmsson format selecton The procedure of selectng F-PDCH transmsson format for each data user s as follows: 1. Calculate the numer of Walsh codes and power used for the voce users. 2. For each possle slot duraton, determne the overhead power requred for F-PDCCH and Forward Common Power Control Channel (F-CPCCH). 3. The leftover power can then e allocated to the F-PDCH. Calculate the avalale C/I for F-PDCH ased on the C/I feedack from R-CQICH of the target MS. The C/I feedack s fltered wth an IIR flter. 4. The encoder packet sze and the numer of slots can e determned for a target PER of 1% ased on the avalale Walsh codes and the avalale C/I for the F-PDCH. 5. In case of retransmsson, the same encoder packet sze as n the ntal transmsson s kept and the aove rate selecton procedure s repeated PER calculaton 1. The aggregate E / for the su-packet s calculated as where E / N t N t n 1 N ( E = 10log10 N = α ( Es 1 / Nt ) s / N ) t, ( E s / N t ) s the SIR per modulaton symol for slot N s the numer of modulaton symols n slot α s the de-mappng penalty for slot f ( E s / N t ) hgher order modulaton than QPSK s used [3] n s the numer of slots transmtted N s the encoder packet sze (ts) 2. A ased con s tossed to decde the outcome (success or falure) of the transmsson ased on the look-up tale and the E / s calculated. N t 3.2 Modelng of Control Channels The forward lnk common control channels such as the Plot, Pagng and Sync channels are assumed to take 20% of the total ase staton transmsson power durng the smulaton tme. The control channels such as F-PDCCH and F-CPCCH are dynamcally modeled n the smulaton. 3.3 Proportonal Far Scheduler For each user wth data n the uffer, a prorty functon s computed and the user wth the hghest prorty s scheduled for transmsson. The prorty functon for user at tme k s computed as: where R ( k) P ( k) = T ( k) α f

3 R (k) s the potental achevale data rate. It s computed usng the fltered C/I feedack from R- CQICH. Note that t s computed assumng full uffer for the MS T (k) s the farness throughput α = f = 1 for all users,.e., the scheduler treats all users equally regardless of ther traffc types. 4. SIMULATION PARAMETERS Both the channel models and traffc models are specfed n [3] and also descred n the followng. 4.1 Channel Models A channel model corresponds to a specfc numer of paths, path delay and power profle (ITU mult-path models), and Doppler frequences for the paths. Tale 1 lsts the channel models assocated wth the assgnment proaltes used n the smulatons. The channel models are randomly assgned to the varous users accordng to the proaltes. Due to the lnk adaptaton nature of the 1XEV-DV system, users wth low speed and sngle fnger (e.g., Channel A) tend to perform etter than users wth hgh speed and multple fngers (e.g., Channel C). Channel Model Tale 1 Channel Models Mult- Path Fngers Speed (km/h) Fadng A Ped A 1 3 Jakes 0.30 B Ped B 3 10 Jakes 0.30 C Veh A 2 30 Jakes 0.20 D Ped A Jakes 0.10 E 1 path 1 0, fd = 1.5 Hz 4.2 Traffc Models Rcan K = 10 db Assgnment Proalty 0.10 Tale 3 Smulaton Parameters Parameters Value Comment Max C/I 13 db Transmt dversty Off N-channel HARQ N=4 Physcal Layer HARQ C/I feedack delay 3 slots Retransmsson delay 3 slots Rado confguraton 3 Voce servce Smulaton tme 600 seconds 5. SIMULATION RESULTS For Rado Confguraton 3 (RC3) wthout transmt dversty, the voce capacty s 14 users/carrer/sector ased on the requrement from [3] accordng to our smulatons. For mxed voce and data smulatons, the system s loaded wth 50% of the full voce capacty, whch s equvalent to 7 users/carrer/sector. The numer of data users s vared n the smulatons n order to get to the target outage level. 5.1 Voce servce results Hstogram of voce data rates Fgure 1 shows the hstogram of data rates for a random selected voce user. As can e seen from the fgure, the percentage of the full rate, half rate, quarter rate, and eghth rate frames follow those specfed n [3] (.e., 29%, 4%, 7%, and 60% for RC3 full rate, half rate, quarter rate, and eghth rate, respectvely). The traffc models nclude WAP, Near Real Tme streamng vdeo (NRT), HTTP and FTP. The detal statstcs of the traffc models are descred n [3]. The assgnment proaltes for each of the traffc models are provded n Tale 2. Tale 2 Traffc Models Traffc Model Assgnment Proalty WAP NRT HTTP FTP Other Smulaton Parameters Whle there are many dfferent parameters that can e defned n the performance evaluaton [3], the most notale parameters are lsted n Tale 3. Fgure 1 Hstogram of Data Rates, 50% Voce Users Outage proalty The outage defnton for voce users can e found n [3]. The outage proaltes for all voce users are plotted n Fgure 2. From the fgure we oserve that most of the users have outage level less than 1%. Outage typcally occurs when one or more

4 users n the same sector are n a ad rado lnk condton for a long perod of tme Data throughput per user The data throughput of a user s defned as the rato of the numer of nformaton ts that the user successfully receves and the smulaton tme. The packet delay of a user s defned as the rato of the accumulated delay for all packets of the user and the total numer of packets of the user. The full pcture and zoom-n pcture of data throughput vs. packet delay for each user are depcted n Fgure 4 and Fgure 5, respectvely. From the full pcture we can see that FTP users normally have hgh data throughput as well as long packet delay. We oserved from the zoom-n pcture that NRT users normally have data throughput around 32 kps wth packet delay less than 200 mllseconds. NRT users wth lower data throughput and hgh packet delay are outage users. Note that the source rate for near real tme servce s 32 kps accordng to the traffc model specfed n [3]. The data throughput for WAP users s typcally less than 5 kps wth packet delay less than 300 mllseconds. The low data throughput s due to the low traffc load for WAP users. Fgure 2 Outage Proalty, 50% Voce Users 5.2 Data servce results Sector throughput and outage The sector throughput s defned as the numer of nformaton ts that a sector can delver correctly to all data users t serves. The outage defnton for data users s specfed n [3]. The data throughput and outage vs. numer of data users s shown n Fgure 3. As the numer of data users ncreases, the data throughput ncreases from 270 to 335 kps/carrer/sector wth 50% of full voce capacty. The system outage also ncreases from 2.1% to 3.5%. Fgure 4 Data Throughput vs. Packet Delay: Full Pcture Fgure 3 Data Throughput and Outage vs. Numer of Data Users Fgure 5 Data Throughput vs. Packet Delay: Zoom-n Pcture

5 5.2.3 Packet call throughput per user The packet call throughput of a user s defned as the rato of the numer of nformaton ts that the user successfully receves and the accumulated delay for all packet calls of the user, where the delay for an ndvdual packet call s defned as the tme etween the frst packet of the packet call enters the queue for transmsson and the last packet of the packet call s successfully receved. The packet call delay of a user s defned as the rato of the accumulated delay for all packet calls of the user and the total numer of packet calls of the user. The full pcture and zoom-n pcture of the packet call throughput vs. packet call delay are llustrated n Fgure 6 and Fgure 7, respectvely. From the full pcture we can see that the packet call throughput decreases as the packet call delay ncreases. For FTP users the packet call throughput can e as hgh as 900 kps for extreme cases. The HTTP users have relatvely low packet call throughput and packet call delay compare wth FTP users. Ths s ecause the packet call throughput depends on the lnk speed as well as the traffc load and packet arrval pattern wthn a packet call. The NRT users always have packet call delay of 600 seconds, ths s due to the fact that for NRT users the entre smulaton tme s defned as a packet call. We also oserved from the zoom-n pcture that packet call throughput for WAP users are lower than 5 kps wth packet call delay less than 5 seconds. Agan ths s ecause WAP users have low traffc load and large packet nterarrval tme wthn a packet call. Fgure 7 Packet Call Throughput vs. Packet Call Delay: Zoom-n Pcture 6. SUMMARY The 1XEV-DV system s desgned to provde real-tme crcut servces and hgh data rate packet data servces n the same RF carrer. The system structure of 1XEV-DV s refly ntroduced n ths paper. Smulaton results are provded to characterze the performance of the system. The statstcs of ndvdual users wth dfferent type of traffc are also provded n ths paper. We have shown that wth 50% of the full voce capacty n the network, the system can stll provde the sector throughput of around kps/carrer under the traffc models and channel models specfed n [3]. The packet call throughput can e as hgh as 900 kps for FTP users under extreme cases. Due to the capalty of 1XEV-DV to support oth voce and data servce n the same RF carrer, t allows the wreless operators to utlze ther spectrum more effcently and provdes a means to alance the voce and data load n ther system ased on ther specfc needs. REFERENCES Fgure 6 Packet Call Throughput vs. Packet Call Delay: Full Pcture [1] Physcal Layer Standard for cdma2000 Spread Spectrum Systems Release C, 3GPP2 Document No. C.S0002-C V1.0, May 28, [2] Mole Staton-Base Staton Compatlty Standard for Wdeand Spread Spectrum Cellular Systems, ANSI/TIA/EIA-95-B-99. [3] 1XEV-DV Evaluaton Methodology Addendum (V6), 3GPP2 WG5 Evaluaton Ad Hoc, July 25, [4] Yun, Youngwoo, et. al., Reference Lnk Level Performance Curves of L3NQS Framework Proposal, 3GPP2 Contruton C , July 9, 2001.