1、. I I) t m TIA/EIA ENGINEERING BULLETIN Cellular Mobile Receiver Dynamic Range TSB=35 * APRIL 1992 TELECOMMUNICATIONS INDUSTRY ASSOCIATION z!F!Eia AuMnwacani.crm - STD=EIA TSB-35-ENGL 1992 323Lib00 058Li5b7 ObT M NOTICE # TIA/EIA Engineering Standards and Publications are designed to serve the publi
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8、ime as may be occasioned by changes in technology, industry practice, or government regulations, or for other appropriate reasons. (Formulated under the cognizance of the TIA TR-45-1 Subcommittee on Cellular Radio Equipment) Published by TELECOMMUNICATIONS INDUSTRY ASSOCIATION Engineering Department
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10、*EIA TSB-3S-ENGL 3472 3Z3Lib00 CI584570 883 TSB-35 Page 1 CELLULAR MOBILE RECEIVER DYNAMIC RANGE (Formulated under the cognizance of the TR-45.1 Subcommittee on Cellular Radio Equipment) Recently various cellular carriers and their customers have been experiencing degraded mobile unit receiver perfo
11、rmance when these units are operated in close proximity to certain cell sites belonging to the competitive system. Typical complaints are of dropped or noisy calls or even total loss of service. It has been suggested that the cause of these problems is noise and/or intermodulation products emanating
12、 from the nearby cell. A more likely cause, as we will discuss below, is a lack of sufficient dynamic range in the mobiles receiver front end. Cellular mobile and portable units are designed to operate over both the A and B frequency bands. A mobile may be receiving a voice or control channel from a
13、 cell site some distance away while geographically close to a cell site of the competing service. In any case, the mobiles receiver front end (RF preamplifier and first conversion mixer) must handle the strong signal from the nearby site without losing significant sensitivity for the relatively weak
14、 signal it is trying to capture. In order to do this, the amplifier and mixer must operate linearly over a wide range of input signai levels. This is called the receivers dynamic range. When input signals exceed the receivers dynamic range, intermodulation products (IMPs) are generated which appear
15、as interfering signals in following receiver stages. If the IMPs do not fall on the same frequency as the desired signal, or are at a level well below that of the desired signal, no harm is done. However, if a relatively strong IMP falls within the band to which the receiver is tuned, it will cause
16、the same sorts of problems as excessive CO- channel interference - noisy and/or dropped calls. If one of the strong input signals responsible for the offending IMP is a control channel, a scanning mobile might “lock onto“ the IMP, and appear to “roam“ even though tuned to one of its “home“ system co
17、ntrol channels. The developers of cellular were aware of this potential problem, and established standards for mobile receiver dynamic range. In the case of the original AMPS specification, the dynamic range requirements were mandatory, while those of the ELA industry standard IS- 19-A (covering cel
18、lular mobile unit performance) are “recommended.“ FCC type acceptance rules do not establish minimum receiver performance. TSB-35 Page 2 Copies of the relevant sections of both AMPS and IS-19-A specifications ar attached. Both specify receiver dynamic range by means of a test that measures the degre
19、e to which a receiver generates IMPs in the presence of two strong signals offset in frequency from the one that is tuned. At first observation, it appears that the two requirements are the same: generated IMPs are at least 65 dB attenuated from the level of the causal input signals. In reality, how
20、ever, the AMPS specification is much tougher, because its test is concerned with IMPs at a level of -100 dBm, while the IS-19-A test involves IMPs near the receivers 12 dB SINAD sensitivity point, which is typically -116 dBm. The big difference between these two specifications is that, once signals
21、input to the receiver exceed its dynamic range, making those signals just a bit stronger causes levels of the resultant IMPs to increase substantially. Typically, a ten dB increase in IMP level is caused by only a 4 dB increase in the two causal input signals. In the IS-19-A test, an IMP of around -
22、120 dBm will reduce SINAD to 12 dB. For a mobile just meeting the specification, this will be caused by a receiver input level of around -48 dBm. In the AMPS test, the desired signal level needed to bring receive SINAD to 12 dB will be around -97 dBm in the presence of IMP producing signals no lower
23、 than - 35 dBm. If a mobile just meeting the IS-19-A requirements is subjected to IMP producing signals at this -35 dBm level, however, the IMP levels will be a around -88 dBm, and will reduce SINAD to 12 dB for an input level of the desired signal of about -85 dBm. To illustrate the impact of this
24、difference, consider what happens when a mobile operates near a competitive cell site. Worst case, the mobile front end may be subjected to signals from that site up to, say, -35 dBm. If the mobile was designed to AMPS specification, it would probably be able to operate on desired signal levels as l
25、ow as around -90 dBm, taking into account fading margin. In an interference limited system, this should be adequate performance. However, if the mobile was only designed to IS-19-A specifications, under the same circumstances the received level of the desired signal would need to be no lower than ar
26、ound -77 dBm. This sort of signal level is commonly encountered, even in interference limited systems. The potential problems from intermodulation in subscriber unit front ends has been brought to the attention of TIA subcommittee 45.1, which maintains IS-19. That body has made modifications to IS-1
27、9 that will result in a higher recommended performance level for intennodulation rejection. These modifications should take effect in the near future with the release of IS-19-B. System operators must, however, cope with the existence of large numbers of subscriber Units designed to the current IS-1
28、9-A recommendations. These units may exhibit poor receiver operation in areas where signals from a competitive cell site are both very strong and signifcantly stronger than the signals received from the serving cell site. To reduce the incidence of poor senrice due to mobile front end intermodulatio
29、n, cellular operators may wish to engineer their systems so as to limit the areas where such problems may occur. in the largest cellular markets, this might require cooperation between the competitive carriers for purposes of coordinating location and transmit power of cell sites. . - STD-EIA TSB-35
30、-ENGL 1772 3234b00 0584572 b5q TSB-35 Page 3 PERTINENT SPECIFICATIONS From Advanced Mobile Phone Service, Inc.: Eauipment Specification, April i983 Preliminary Ce llular Mobile TeleDhone 3.2.6.1 Intermodulation Performance. When subjected to an input of two unmodulated RF signals each having -35 dBm
31、 amplitude and spaced 60 and 120 kHz either above or below the desired channel center frequency, the input signal amplitude of the resulting on-channel intermodulation product measured by the receiver signal strength indicator (see section 3.2.4) shall not exceed -100 dBm. This is an intermodulation
32、 conversion loss of 65 dB. From EL4 Interim Standard IS-19-A. March 1987 2.3.3 intermodulation Spurious Response Attenuation 2.3.3.1 Definition The intermodulation spurious response attenuation of the receiver is the measure of its ability to receive a modulated input RF frequency in the presence of
33、 two unmodulated interfering signals so separated from the assigned input signal frequency and from each other that the nth order mixing of the two undesired signals can occur in the non-linear elements of the receiver, producing a third signal whose frequency is equal to that of the assigned input
34、RF signal frequency. 2.3.3.2 Method of Measurement Disable the expandor, terminate the audio output of the receiver in its normally intended load, and make measurements using a C-message weighted filter. Equally couple three RF signal generators to the receiver antenna input terminals. Modulate the
35、first RF signal generator to k8-kHz peak frequency deviation with 1000 Hz. Leave the second and third RF signal generators unmodulated. Turn off the second and third RF signal generators. Adjust the frequency of the first RF signal generator to the assigned input RF signai frequency, and adjust the
36、output to give 12- dB SINAD as in 2.3.1.2. Record this level as the reference sensitivity. Increase the output level of the first RF signal generator to 3 dB above this reference sensitivity. TSB-35 Page 4 Adjust the second RF signal generator to a channel 60 kHz above the assigned input frequency,
37、and adjust the third RF signal generator to a channel 120 kHz above the assigned input frequency. Turn on the second and third RF signal generators, maintain their outputs at equal levels, and increase these levels until the SINAD measurement from the desired RF signal generator is reduced back to 1
38、2 dB. Adjust the frequency of either of the interfering RF signal generators slightly to produce the maximum interfering signal before the final measurement is made. Record the RF signal level of the two interfering signal generators. Repeat the above measurement with the second RF signal generator
39、set to 60 kHz below and the third RF signal generator set to 120 kHz below the assigned input frequency. The smaller of the ratios of the signal level of the second and third RF signal generators to the reference sensitivity level of the first RF signal generator expressed id dB is the measure of intermodulation spurious response attenuation. 2.3.3.3 Minimum Standard The intermoddation spurious response attenuation shall be at least 65 dB. STD-EIA TSB-35-ENGL 1772 m 3234b00 058Li574 Li27 m
