Interpreting CDMA Mobile Phone Testing Requirements

Transcription

1 Appliation Note 54 nterpreting CDMA Mobile Phone Testing Requirements Most people who are not intimately familiar with the protool involved with S-95A & J- STD-008 (CDMA) phones will enounter some onfusion when interpreting the minimum perfmane standards of S-98A/J-STD-018 f the first time. n der to ondut testing, CDMA tehnology, test standards, and test instrumentation must be understood. The purpose of this appliation note is to failitate understanding of CDMA test parameters and how to apply these parameters to a speifi test setup in der to exeute S-98A ompliant tests. Test Setup Although S-98A requires multiple test setups, the most typial test setup is shown Figure 1. n this onfiguration, a base station emulat, an RF hannel emulat, a C/N emulat, and a mobile phone are required. This test setup an be easily reognized by using ommerially available test equipment (See Figure 2). n this example, we will use a base station emulat, a TAS 4500 RF Channel mulat, a TAS 4600 Noise and nterferene mulat, and a dual juntion irulat f interfaing to the mobile phone s duplex pt. F me infmation on the irulat, please refer to the Notes on Testing setion. Figure 1. xample of Funtional Test Setup from S-98A Figure 2. Test Setup f S-98A Compliane Testing 2001, Spirent Communiations of atontown, LP (DBA TAS)

2 nterpreting CDMA Testing Requirements Desription of Test Parameters An example set of test onditions that will be used throughout this doument is shown in Table 1. The infmation in this table is taken diretly out of S-98A, setion titled Demodulation of Fward Traffi Channel in Additive White Gaussian Noise n der to begin testing, the parameters in Table 1 must be understood. Unftunately, the parameters in this table do not give all the infmation to neessary to onfigure your test setup. By using these values and some basi CDMA onepts, the other neessary parameters an be derived. The next setion will give a desription of the test parameters. n addition, the parameters that are implied in this table will be explained. Parameter Units Test 7 Test 8 Test 9 / o db 4 Pilot / db -7 Traffi / db o dbm/1.23 MHz -59 Data Rate bps Traffi b /N t db Channel Simulat Configuration 3 Table 1. Demodulation of Fward Traffi Channel in AWGN Tests NOT: The Traffi b/nt value is alulated from the parameters in the table. t is not an adjustable parameter. o The power spetral density of a band limited white noise soure (simulating interferene from other ells) as measured at the mobile station antenna onnet. S-98A speifies that the noise soure used must have a noise bandwidth greater than 1.8 MHz. t is imptant that the noise soure be suffiiently wide to simulate interferene from other ells. An even wider noise soure (>10 MHz) will have the added benefit of testing the reeiver s ability to rejet broadband noise. A 5 MHz plot of the TAS 4600 noise soure is shown in Figure 3. The o parameter, along with the /o (signal-to-noise) value defines the hannel power, and the arrier-to-noise ratio parameters to be set in the TAS 4600 Noise and nterferene mulat. Figure 3. Spetrum of TAS 4600 Broadband Noise Soure 2

3 nterpreting CDMA Testing Requirements Desription of Test Parameters - Continued / o The fward hannel signal-to-noise ratio f a 1.23 MHz bandwidth. This parameter is set in the 4600 with the C/N parameter. Sine a CDMA signal is noise like, and sine CDMA is designed to operate at a low signal-to-noise ratio, it is diffiult to view the CDMA arrier signal with additive noise present on a spetrum analyzer. Figure 4 shows two plots of an impaired CDMA hannel at a 4 db signal-to-noise ratio. The first plot uses the default analyzer settings. t is obvious that the CDMA hannel is indeed diffiult to find. The seond plot in Figure 4 shows the same signal on an expanded sale with 16 times video averaging. Figure 4. CDMA Channel with Broadband Noise (4dB Signal-to-Noise Ratio) Pilot / The fration of the total base station transmitted power dediated to the pilot hannel. This level will be set diretly in the base station emulat. n the example listed in Table 1, the pilot level would be set to -7 db. This level tells the base station emulat to dediate 1/5 of the total transmit power () to the pilot hannel. n S-98A the levels of the various omponents of the total transmit power are speified as the fration of the total transmit power. The sum of these frational parts should add up to 1. Setion of S-98A uses the following quation # 1 to relate the various levels of the total base station transmit power. quation # 1: Pilot Syn Paging Traffi Power Control OCNS = 1 3

4 nterpreting CDMA Testing Requirements Desription of Test Parameters - Continued Traffi / The fration of the total base station transmitted power dediated to the fward traffi hannel. This level will also be set in the base station emulat. n some base station emulats, the traffi level that is set refers to full rate traffi only, where full rate is 9600 bps f rate set 1, and bps f rate set 2. Thus, a retion is needed when using data rates that are not full rate. F example, in test 9 above, the data rate is 1200 bps, eighth rate. n this ase the traffi level that would be set in the base station emulat is shown in quation #2. Data Rate quation # 2: Traffi -10log 10 (frational rate) = (-9) = -12.3dB The number of bits per seond of infmation being transmitted on the fward traffi hannel. This value is set in the base station emulat. Typially, the rate set and the frational rate is programmed into the base station emulat. Rate set 1 s full rate is 9600 bps, while rate set 2 s full rate is bps. 4800, 2400, and 1200 bps respond to 1/2, 1/4, and 1/8 rate on rate set 1, while 7200, 3600, and 1800 bps respond to 1/2, 1/4, and 1/8 rate on rate set 2. The data rate affets the alulation of Traffi b/nt, and an also affet the traffi level programmed into the base station emulat (see Traffi / above) quation # 3: Traffi Traffi b / N t = 10log10 o data rate Traffi b /N t The effetive bit energy to noise density of the fward traffi hannel. As Table 1 shows, this number is not a settable parameter, but is in fat a funtion of the other parameters in the table. This number an be alulated using quation #3. F example, in test 7 listed in Table 1, the Traffi b/nt would be alulated as shown in quation #4. quation #3 f Traffi b/nt is valid only f the ase of one path hannel simulat onfigurations. Calulation of the Traffi b/nt f 2 and 3 paths f the hannel onfigurations given in S-98A an be alulated using the fmulas in setion of S-98A. quation # 4: Traffi b /N t = (4) (-14.4) 10log 10 (256) = 13.68» 13.7 db Channel Configuration One of five standard onfigurations shown in Table 2 (from S-98A). This infmation is programmed into the TAS 4500 RF Channel mulat. Channel mulat Configuration Vehile Speed [km/hr] Number of Paths Path 2 Power (Relative to Path 1) [db] 0 0 N/A 0 0 Path 3 Power (Relative to Path 1) [db] N/A N/A N/A -3 N/A Delay from Path 1 to nput (us) Delay from Path 2 to nput (us) 2 2 N/A 2 2 Delay from Path 3 to nput (us) N/A N/A N/A 14.5 N/A 4

5 nterpreting CDMA Testing Requirements Desription of mplied Parameters Paging / Power Control / This is the total transmit power spetral density of the fward hannel. This value is not expliitly stated in the test tables, but an be derived from other infmation in table. F example, in the tests listed in Table 1, the signal-to-noise ratio (/o) is given as 4 db, and the reeived power spetral density of the bandlimited white noise is given as -59 dbm/ 1.23 MHz. Thus, would be alulated as shown in quation #5. This value f the total transmit power is then programmed into the TAS 4600 Noise and nterferene mulat as the arrier power level. quation # 5: = / o o = (-59) (4) = -55 dbm The paging hannel makes up a ption of the total fward transmit power. The paging hannel arries various ontrol and page messages from the base station to the mobile station. Although not stated expliitly f eah test, the paging level should be set to - 12 db (1/25) of the total transmit power unless otherwise speified. Syn / The syn hannel arries the synhronization message to the mobile station on a dediated hannel. Although not stated expliitly f eah test, the paging level should be set to - 16 db (1/40) of the total transmit power unless otherwise speified. The losed loop power ontrol bits are sent on the fward traffi hannel. Fward traffi hannel bits are puntured (removed) and replaed by power ontrol bits every 1.25 ms. This is not a settable parameter in the base station emulat. However, its value an be alulated from equations in setion of S-98A. OCNS / The OCNS is the Orthogonal Channel Noise Simulat, a hardware mehanism used to simulate users on other thogonal hannels of the fward CDMA hannel. The OCNS makes up the remainder of the total transmit power, and is typially automatially set as suh in the base station emulat. Notes on Testing The pilot level and the data rate an be diretly programmed into the base station emulat. The traffi level entered into the base station emulat, should have appropriate ompensation f the fat that the traffi level is based on full rate transmission. Thus, 3, 6, 9 db should be added to the traffi level listed in the table f 1/2, 1/4 and 1/8 rates respetively. Sine the base station emulat is not onneted diretly to the devie under test, it is imptant to arefully onsider its output power. n the ase of the test setup shown in Figure 2, a nominal output power of -10 dbm would satisfy the input requirements of the TAS 4500 RF Channel mulat. The absolute power level,, would be set later in the test hannel by the TAS 4600 Noise and nterferene mulat, beause using the TAS 4600 to set the fward hannel power will provide the best auray. The arrier frequeny entered into the TAS 4500 RF Channel mulat and the TAS 4600 Noise and nterferene mulat an be alulated from the hannel number, N, using quation #6. n the blok diagram of the test setup in Figure 2, a Ma-Com 7R193 dual juntion irulat is used to interfae to the duplex pt on the mobile phone. The high isolation juntion of the dual juntion irulat should be used between the phone and TAS A high powered signal leaking bak into the TAS 4600 ould result in intermodulation produts. The high isolation of the dual juntion irulat will insure that very little mobile transmit power leaks bak into the noise and interferene emulat. This setions summarizes the onfiguration f the TAS 4500 and the TAS n Table 3 & 4, the onfiguration and parameters of both instruments are provided. quation # 6: 0.030N MHz Center Frequeny = 0.030(N -1023) MHz 1 N N

6 nterpreting CDMA Testing Requirements Summary of Parameter Setup f TAS 4500 and Tas 4600 Table 3. TAS 4500 Parameter Configuration TAS 4500 Configuration Configuration Veloity Units = km/h mulation Method - Jakes Nominal Fading Repetition - 20 minutes Crelation Algithm - nvelope Channel 1 nput Referene Level dbm Output Attenuat 0 dbm LO Mode internal auto Carrier Freq. (MHz) Path Status on off off off off off Relative Delay (us) Modulation Type Rayl Doppler Freq. (Hz) Veloity (km/h) Fading Power Spetrum C Relative Loss (db) Log-nmal Freq. (Hz) Log-nmal STD (db) Table 4. TAS 4600 Parameter Configuration TAS 4600 Configuration Carrier to Noise Units C/N Noise Generat Units - nterferene Soure A Status off nterferene Soure B Status off mpairments CH1 off mpairments CH2 - Channel 1 2 Carrier Freq. (MHz) mulation Mode C/N - Reeiver Bandwidth (MHz) Carrier to Noise Ratio (db) Bit Rate (bps) - - b /N o Ratio (db) - - C/N o (db) - - C/ (db) - - Noise Power Density (dbm) - - Output Level (dbm) Measure Monit Point CH1 # Averages 16(2 4 ) Duty Cyle 100% Spirent Communiations of atontown, LP (DBA TAS) 541 ndustrial Way West, atontown, NJ 07724, U.S.A. Phone: (732) , Fax: (732) , 6 Spirent Communiations is a trademark and servie mark of Spirent pl. All rights reserved Speifiations are subjet to hange without notie, Printed n U.S.A., 2/01 v.2