XR1002-QB Datasheet, PDF (9/10 Pages) Mimix Broadband – 18.0-30.0 GHz GaAs Receiver QFN, 7x7 mm

18.0-30.0 GHz GaAs Receiver
QFN, 7x7 mm
November 2006 - Rev 03-Nov-06
R1002-QB
Tech Note [1] Assumptions on Modulation - The effect of intermodulation on the performance of a QAM radio is determined by
many factors. By making some reasonable assumptions, it can be deduced that the XR1002 will conform with ETSI-specified high
receive power requirements when operating in radios with modulations of up to 256QAM and higher.
For a Gray-coded QAM signals passing through a AWGN channel, an optimal receiver will require the C/N ratios shown in
Figure 1.
QAM level C/N for
Assumed IM3
IIP3 for
1E-3(dB)
for 1E-3 (dBm)
1E-3 (dBm)
16
16.6
-39.6
-14.7
64
22.6
-45.6
-11.7
128
25.6
-48.6
-10.2
256
28.6
-51.6
-8.7
Figure 1: C/N and IM3/IIP3 values for QAM (Pin=-20dBm and BER=1E-3)
To estimate the IM3 required to produce a BER of 1E-3 involves many approximations, and assumptions on the radio and modem
characteristics. Following is an example which is based on the assumptions listed. All of the values of 'Assumed IM3 for 1E-3' listed
in Figure 1 are derived using this method.
For a total input power at the receiver of -20dBm, this equates to a per-tone level of -23dBm, for a two-tone input. From Figure 1, an
optimal 64 QAM receiver will require a 22.6dB C/N for a 1E-3 BER [F].Therefore, the assumed in-band IM3 for 1E-3 performance is
-23 - 22.6 = -45.6dBm. From this, the required IIP3 for 64 QAM is -23 + 22.6/2 = -11.7dBm.
Assumptions:
[A] The C/N figure for 1E-3 BER assumes a matched receiver with no implementation loss, and no degradation due to phase noise.
[B] All third order intermodulation falls in the pass-band. In reality, some of the intermodulation will fall in the adjacent channels, and
can be removed by filtering. This assumption makes this analysis conservative.
[C] The amplitude distribution of the distortion products can be approximated to that of thermal noise. There is a relatively high
degree of uncertainty in this assumption as the peak to average ratio for the signal depends on alpha, and the statistics of the
third order signal distortion are unknown.
[D] The addition of interference at a level of 6dB below the AWGN due to the channel, increases the effective noise by 1dB.This is
true if the interference has identical Gaussian statistics to the channel's AWGN.
[E] The receiver input level range is set at an upper limit of -20dBm for 1E-3 BER performance [1][2][3].This input level is referenced
before the branching [1][2][3], which in reality may bring the upper limit down below -21dBm. The exact number will depend on
the particular system, so a worst-case hypothetical situation of no branching loss will be assumed.
[F] The 1E-3 BER performance can depend greatly on the presence and performance of FEC.The worst case situation of NO FEC has
been assumed in these derivations.
References:
[1] ETSI EN 300 198 V1.4.1 (2001-02): "Fixed Radio Systems; Point-to-point equipment; Parameter for radio systems for the
transmission of digital signals operating at 23 GHz"
[2] ETSI EN 300 431 V1.3.1 (2001-02): "Fixed Radio Systems; Point-to-point equipment; Parameters for radio system for the
transmission of digital signals operating in the frequency range 24,5 GHz to 29,50 GHz"
[3] ETSI EN 300 197 V1.5.1 (2001-10): "Fixed Radio Systems; Point-to-point equipment; Parameters for radio system for the
transmission of digital signals operating at 32 GHz and 38 GHz"
Mimix Broadband, Inc., 10795 Rockley Rd., Houston, Texas 77099
Tel: [phone] Fax: [phone] mimixbroadband.com
Page 9 of 10
Characteristic Data and Specifications are subject to change without notice. ©2006 Mimix Broadband, Inc.
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