On the Design of a Configurable UMTS/NAVSAT Transceiver

Transcription

1 On the eign of a onfigurable UMT/VT Tranceiver Linu Maurer, E, Linz, utria, ndrea pringer, Rainer tuhlberger, hritian Wicpalek, ntitute for ommunication and nformation Engineering, Univerity of Linz, utria, Guenter Heinrich and Jón Winkel, fe GmbH, Germany hritian rewe, nfineon Technologie G, Germany linu.maurer@infineon.com BTRT Thi paper introduce a combined UMT/VT receiver architecture. fter a review of the tate-of-the-art, a configurable UMT/VT architecture i propoed. The invetigated concept i baed on a reconfigurable receive chain to prevent duplication of hardware, which will reult in coniderably lower cot. The bigget challenge in the deign of VT receiver are the extremely tight noie figure (F) requirement. nother key iue of integrated UMT/VT receiver i the maximum tolerable UMT tranmit leakage injected into the VT receiver. n analytical derivation of the acceptable UMT tranmitter leakage for a certain ranging degradation i given. Thee value are compared with meaured leakage value baed on power amplifier (P) and urface acoutic wave (W) filter for UMT.. TROUTO avigation and location baed ervice will be a key buine driver in the field of mobile communication. Therefore, cellular phone and peronal digital aitant (P) will become the market leader in the area of peronal navigation application. Market urvey forecat that the global GP receiver market for automotive and mobile phone application could reach around 55 million unit in 5. bout 73% of thi market, correponding to around 4 million unit, i expected to fall into the category of mobile phone application. The planned global navigation atellite ytem (G) modernization will undoubtedly further expand and improve application for uer in many field by allowing combined ue of uch ytem in hybrid receiver. Thee G advance include the implementation of the Galileo ytem, now entering the development and validation phae under the cooperative management of the European ommiion (E) and the European pace gency (E), a well a planned improvement in the U.. counterpart, GP. Taking all thi into account, a combined olution of communication and navigation will be a key buine in the future wirele field.. YTEM OVERVEW. ellular Table 1 how the paired frequency band for UTR/F (UMT Terretrial Radio cce / Frequency iviion uplex). Operating Band UL Frequencie UE tranmit, ode B receive L frequencie UE receive, ode B tranmit MHz MHz MHz MHz MHz MHz V MHz MHz V MHz MHz V MHz MHz Table 1: Frequency band of the UTR/F. The UMT air interface ue Wideband ode iviion Multiple cce (W-M), baed on irect equence pread pectrum (-). With - each uer ignal i pread by a uer pecific code. The mot prominent advantage of -ytem for cellular ytem i it ability to eliminate the effect of multipath propagation by uing a RKE receiver in the mobile tation. The choice of the uer-pecific code employed for the preading of the uer ignal greatly influence the overall performance of a M ytem. The orthogonality among the preading code hould be a large a poible. Otherwie the receiver will not be able to eparate the different uer ignal due to multiple acce interference (M). The UMT tandard pecifie a root raied-coine (RR) filter for pule haping, which determine to a large degree the pectral propertie of the UMT ignal. The frequency repone G rc of the RR-filter with roll-off factor, tranition type n (RR for n1, R (raied coine) for n) and chip duration T i defined by n πt 1 α G ( ) co ( rc f T f α T T 1 α f < 1 α 1 + α f 1+ α f > The pa-bandwidth of the above defined filter equal (1+ )/, which reult to.34 MHz for UMT (., T 6 n). n Fig. 1 the impule repone of an RR and an R filter are hown. The R repone reult due to the RRfiltering in the tranmitter and the receiver (matched filter). t i clearly viible, that only the R repone i free.

2 (zero croing exactly at multiple of T ). n important iue for the deign of the analog tranceiver i the peak to average power ratio (PR). ue to the QPK-like modulation format of the UMT uer ignal and the fact that everal uer and control ignal are ummed up before converting them to the analog/rf-domain, the PR can grchtl 1.8 E6: two independent BPK(5) ignal, one with data modulated onto the code and one without data. L1: two independent BO(1,1) ignal, one with data modulated onto the code and one without data. For conumer application in general and the tranportation and tourim application, which are the main focu of the GW project, in particular, the navigation ignal tranmitted at the L1 ( MHz) carrier will be the one of highet commercial interet Fig. 1: R and RR (dahed line) impule repone. tê@t eaily reach 9 db with maximum of about 14 db for the downlink (L) and 4 db with a maximum of about 6.5 db for the uplink (UL). B. VT Fig. how the frequency band of the Galileo ignal tructure. E5a E5b E6 E L1 E O/ BPK(1) ymbol rate: 5 p 31 MHz Q-channel -channel O BPK(1) ymbol rate: 1 p The Entire E5 pectrum i Modulated a two ltbo(15,1) in an 8-PK Modulation MHz ommercial ervice BPK(5) Pilot channel: BPK(5) -channel O/ Pilot channel: BO(1,1) 8 MHz Q-channel Fig. : Overview of the current tatu of the Galileo ignal tructure. The following modulation are foreeen for the non-pr Galileo ignal: ltbo(15,1) modulated ignal uing an 8-PK modulation. Thi modulation will be applied to the entire E5 band. t can be hown that the E5a and E5b can be tracked individually a Binary phae-hift keying with a chip-rate of 1.3 MHz BPK(1). BPK(5): Binary phae-hift keying with a chip-rate of MHz. Thi will be realized in a o-called oherent daptive ub-carrier Modulation (M) (thi i required becaue of the third PR ignal on the ame frequency). BO(1,1): Binary offet carrier with a chip-rate of 1.3 MHz, onto a quare-wave with a frequency of 1.3 MHz. Thi i alo known a Mancheter coding. Thee two ignal will alo be part of a M. n the receiver thi can be treated a the following ignal: E5b: BPK(1) modulated ignal with data modulated onto the preading code. E5a: BPK(1) modulated ignal with data modulated onto the preading code. E5a and E5b: ltbo(15,1) modulated in QPK with no data modulated onto the preading code.. TTE-OF-RT REEVER. ellular The homodyne receiver tructure (alo called zero-f or direct-converion architecture) depicted in Fig. 3 i the tate of the art receiver tructure for UMT. The key advantage i the circumvention of the image ignal becaue ω F i. a reult no image filter i required. Thi may alo implify the L (Low oie mplifier) deign becaue there i no need for the L to drive a 5Ω load, which i often neceary when dealing with image rejection filter. econdly, the F-filter, which i uually an external W-filter, and the F-amplifier can be replaced by low-pa filter and baeband amplifier that are amenable to monolithic integration. Thi topology alo entail a number of iue that do not exit or are not a eriou in other receiver tructure. ince in a homodyne topology the downconverted band extend to zero frequency, offet voltage can corrupt the ignal and, more importantly, aturate the following tage. There are three main poibilitie how offet are generated. Firt, the iolation between the LO port and the input of the mixer and the L i not infinite. Therefore, a finite amount of feedthrough from the LO port to the mixer or the L input alway exit. Thi LO leakage arie from capacitive and ubtrate coupling and, if the LO ignal i provided externally, bond wire coupling. Thi leakage ignal i now mixed with the LO ignal, thu producing a component at the mixer output. Thi phenomenon i called elf-mixing. imilar effect occur if a large interferer leak from the L or mixer input to the LO port and i multiplied by itelf. time varying offet i generated if the LO ignal leak to the antenna and i radiated and ubequently reflected from moving object back to the receiver. 9 Fig. 3: irect converion receiver architecture. Q

3 Large amplitude modulated ignal that are converted to the baeband ection via econd order ditortion of the Q mixer may alo lead to time varying offet. n order to prevent thi kind of offet, a large econd order ntercept Point (P) of the Q mixer i neceary. UMT compliant receiver need approximately 8 db of gain. Mot of thi gain i contributed by the baeband amplifier. That mean that even mall offet (in the range of everal mv) at the mixer output may lead to level ufficient to aturate the. The natural olution for offet cancellation i high-pa filtering. Thi approach i only poible becaue of the wideband nature of the UMT ignal. Other critical iue for the zero-f receiver topology are Q mimatche and flicker noie. Epecially the latter one i highly problematic, if very low noie figure are required and/or the bandwidth of the wanted ignal i in the ame order of magnitude a the bandwidth in which the flicker noie i dominant. B. VT tate-of-the-art GP receiver front-end are baed on a low-f architecture (ee Fig. 4). Thi architecture comprie all benefit for a low-power, high-integration olution in complementary metallic oxide emiconductor (MO) technology while circumventing the aforementioned problem of a zero-f architecture, uch a dc-offet, flicker noie and econd harmonic ditortion. The bandwidth of the RF front-end i approximately 4 MHz, to include the two main lobe of the Galileo ignal a well a the main lobe of the GP / code with two ide lobe. Fig. 4: Low-F Front-End rchitecture. One major problem arie by the effect of elf-mixing. The local ocillator (LO) and the LO-ignal which i coupled into the RF caue a fluctuating -offet in the baeband. the main lope of the GP-ignal lie around Hz it would be everely degraded. The choen low-f architecture prevent thi diadvantage by fixing the navigation ignal at an F of 3.5 MHz. nother advantage compared to the zero-f topology i that the flicker noie between and 1 MHz i not a concern. ompared to a receiver with more than one mixer tage no further external filtering i required. The limitation of the F bandwidth i performed by a polyphae filter tage. The ubequent G further amplifie the ignal to a detectable level and guarantee the optimal duty cycle of the three-bit. three-bit quantization reduce the R degradation to le then.7 db. The target for implementation of the receiver frontend i an overall noie figure of db combined with low power conumption. V. PROPOE ELLULR/VT REEVER RHTETURE Within GW, a combined Zero F/Low F Receiver, with a ingle reconfigurable front end, i propoed. With thi concept it i poible to receive UMT-ignal with the Zero F configuration and the Galileo ignal with the Low-F configuration with only one reconfigurable front end. onverting the received G ignal down to a low F largely circumvent the ditortion due to flicker noie. The tructure of the receiver i hown in Fig. 5. epending on what type of ignal i received, the appropriate LO frequency i ued and the analog and digital ignal proceing building block are properly configured. RF-ignal co( ω LO t) 9 in( t) ω LO LO-ignal Fig. 5: Zero F/Low F Receiver Front-End. The main tak of the digital front end (FE) are channel election and decimation. cacaded integrator-comb () filter [3] i ued to decimate the output by an integer factor. hannel election filtering and the final integer decimation are realized by wave digital filter (WF) [4]. finite impule repone (FR) filter i ued to correct the pa-band droop caued by and WF and for pule filtering according to the different tandard. To correct the pa-band group delay ripple, a configurable all-pa (P) filter i ued. For the baeband interface it i neceary to receive the ignal by an integer factor of the ymbol and o a fractional ample rate converion (FR) mut be implemented. For receiving G ignal the FE mut include a digital down converion from low F to baeband. The mode, the filter coefficient and the fractional decimation factor of the FR mut be configured accordingly to enable ignal reception in either UMT or GP/Galileo mode. V. OE TRKG EGRTO UE TO UMT TRMT GL LEKGE RX- FE RX- FE The continuou tranmiion during an active UMT connection ha to be conidered carefully in the deign of a configurable UMT/VT tranceiver. The allowed puriou emiion in the UMT tandard [1] do not Q

4 account for the frequency band allocated for Galileo a decribed in ection. Table how the general minimum puriou emiion requirement for operation in frequency band, which i olely conidered for the work within GW. Frequency Bandwidth Meaurement Minimum requirement Bandwidth 9 khz f < 15 khz 1 khz -36 dbm 15 khz f < 3 MHz 1 khz -36 dbm 3 MHz f < 1 MHz 1 khz -36 dbm 1 GHz f < 1.75 GHz 1 MHz -3 dbm Table : General puriou emiion requirement. ccording to Table 3GPP compliant tranmitter are allowed to have puriou emiion of up to -3 dbm meaured within a meaurement bandwidth of 1 MHz. When the UMT tranmitter i located cloe to the Galileo/GP receiver the ranging accuracy will be degraded. The achievable accuracy uing a coherent LL for the code tracking i given by β / BL (1.5BLT) G ( f ) in ( πf ) df / σ celp, β / π ( ) in( ) fg f πf df / with B L being the noie bandwidth of the LL in Hz, T the ntegration time of the correlator in, the orrelator pacing in, G (f) the pectrum of the ignal in, β the two-ided bandwidth in Hz, and / the arrier-to-noie ratio in db/hz. The pectral denity for BO modulated ignal i given by 1 in( πftc )in( nπftc ) G ( ) co( ) f ntc πf πftc for n even, 1 in( πftc ) co( nπftc ) G ( ) co( ) f for n odd. ntc πf πftc Therefore, the variance of the range i invere proportional to / a can be een in the equation above. Thu, the acceptable ranging degradation of 1 % can be tranlated into a / degradation of.83 db. To etimate the reulting degradation caued by the UMT tranmitter interference the following well-known equation can be ued []: β r / G ( f r / eff β r / β r / ( ) + i G f df / i βr r / ( ) ) df G ( f ) G ( f ) df and G are the carrier power and pectrum of the Galileo/GP ignal, repectively. i and G i are the carrier power and pectrum of the interferer, repectively. n thi cae thi correpond to the puriou emiion requirement. To reduce the out of band interference it i poible to apply filter with high enough out-of band uppreion. To obtain a firt etimate of the tolerable interference we aume that the filter of the G receiver i a brickwall filter, i.e. the filter ha db gain inide the operative band, and the interference from the UMT terminal i wide-band with a contant power pectral denity of n. Under the lat aumption the power pectral denity injected into the Galileo/GP receiver by the UMT tranmitter can be derived in the following way: β / / 1 / umt n β β n β G ( f ) G ( f ) df G ( f ) df G ( f ) df. umt / / / β β f we further aume that the RF-bandwidth β i that large that mot of the ignal pectrum i contained within the integration region, then the effective / further implifie to: : α n 1+ eff n 1 1 α 1 α n + 1 The following Figure how the degradation of /o (Figure 6) and the degradation of the tandard deviation of the peudo range meaurement (Figure 7) a a function of the interfering UMT power pectral denity (1 n. Fig. 6: egradation of the carrier-to-noie ratio in db a a function of the interfering UMT pectral denity (in dbm/hz) for two value of aumed thermal noie denity (o-17 dbm/hz and 175dBm/Hz). Fig. 7: egradation of the peudo-range accuracy a a function of the interfering UMT pectral denity (in dbm/hz) for two value of aumed thermal noie denity (o-17 dbm/hz and 175dBm/Hz).

5 omparing the two figure above, we ee that a degradation of for example 15 db for / will reult in an increae of the tandard deviation on the meaurement (code and carrier) by a factor 6. To keep degradation of the tandard deviation of the peudo range meaurement below 1.5 the UMT tranmit ignal leakage into the Galileo/GP band mut not exceed the range of -175 dbm to -17 dbm. V. MEURE UMT TRMT GL LEKGE We performed a leakage meaurement on a UMT demontrator to verify if the UMT tranmitter leakage power can be uppreed to a value below -175 dbm. Figure 8 how the meaurement etup. ignal generator (Rohde&chwarz MQ) generate an UMT ignal, which i fed into the power amplifier (P). To maximize the enitivity of the pectrum analyzer (Rohde&chwarz FE) a notch-and a W-filter were ued. The notchfilter wa tuned to the tranmit frequency, wherea the W filter attenuated the harmonic of the tranmit ignal. MQ dbm W-M ignal P fc19.5 MHz waveguide circulator ued a iolator 3 dbm waveguide circulator ued a iolator W filter fc4 MHz notch filter fc19.5 MHz FE Fig. 8: Block diagram of the leakage meaurement. The meaurement how that the UMT tranmit leakage power level i around -133 dbm/hz for all frequency band except the E-E1 band (ee Table 3). n the E-E1 band the level i around -19 dbm/hz. Operating Band Galileo Bandwidth UMT noie E5a 1164 MHz < f < 189 MHz -133 dbm/hz E5b 1189 MHz < f < 114 MHz dbm/hz E6 16 MHz < f < 13 MHz dbm/hz E - E MHz < f < 159 MHz dbm/hz Table 3: Meaured noie from the UMT band into the deired GLLEO band. Thu, a uppreion of 37 db to 4 db i needed to keep the UMT leakage power below -17 to -175 dbm/hz. For the E-E1 band the needed uppreion increae to approximately 41 to 46 db. Fig. 9 how the frequency repone of a UMT-W filter, the minimum guaranteed attenuation according to the vendor pecification and the three GLLEO band. Fig. 9 Frequency repone of the W tranmitter filter t i clearly viible that the attenuation of the W filter reache a value of only 5 db at the E E1 Galileo band edge. With thi uppreion the UMT tranmit leakage reache a level of -154 dbm/hz, which i more than the tolerable level of -17 dbm/hz. However, the W-filter uppreion for the other Galileo band i high enough to keep the UMT tranmitter leakage below -17 dbm/hz. Thu, pecial meaure like additional filtering mut be foreeen for the E-E1 band. V. OLUO n important tep into the market for Galileo i the timely availability of hybrid Galileo/GP receiver in combination with wirele communication network poitioning capabilitie for conumer application. We reviewed important ignal format parameter of UMT and Galileo and propoed a cellular/vt receiver architecture baed on a zero-f/low-f receiver in combination with a digital front end. firt evaluation of the UMT tranmitter leakage into the VT receiver, which i one of the key iue for integrated cellular/vt receiver, ha been preented. t how that with a uitable W TX filter in combination with a tandard UMT tranmitter the required leakage uppreion hould be feaible. KOWLEGEMET The work preented in thi paper wa partly funded by the European ommiion within the 5 th Framework Program under T ontract o. T (GW). REFEREE [1] T 5.11: "UE Radio tranmiion and Reception (F)", Releae 6.4, 3GPP, 4. [] John W. Betz; Effect of arrowband nterference on GP ode Tracking ccuracy, O TM, 6-8 January, naheim,, U [3] Eugene B. Hogenauer, n Economical la of igital Filter for ecimation and nterpolation. EEE Tran. On coutic, peech and ignal Proceing, Vol. P-9, o., pr [4] lfred Fettwei, Wave digital filter: Theory and practice, Proc. EEE, Vol.74, o., Feb. 1986