1、 Rep. ITU-R SM.2022-1 1 REPORT ITU-R SM.2022-1 The effect on digital communications systems of interference from other modulation schemes (Question ITU-R 202/1) (2000-2004) TABLE OF CONTENTS PART A Theoretical investigation Page 1 Introduction 3 2 Project work objectives and plan 4 2.1 Project work
2、objectives. 4 2.2 Project work test plan . 4 2.3 Additional project work developed during the project . 5 3 SPW simulation methodology 5 3.1 SPW simulation set up and designs 5 3.1.1 SPW design wanted fixed link of 4-PSK modulation format with a receiver. 6 3.1.2 SPW design wanted fixed link of 16-Q
3、AM-modulation format with a receiver 8 3.1.3 SPW designs of FSK modulation format with a receiver 10 3.2 SER or BER measurement using Monte Carlo method 11 3.2.1 Selecting a method for an evaluation of BER/SER performance of fixed links. 12 3.2.2 BER/SER measurement uncertainty. . 12 3.3 Validation
4、of SPW simulation designs for wanted fixed links of 4-PSK, 16-QAM and FSK modulation schemes. 12 3.3.1 Methodology 13 4 Results 14 4.1 BER/SER performance of wanted fixed links of 4-PSK, 16-QAM and FSK modulation formats. 14 4.2 PSD plots of wanted and unwanted sources . 20 4.3 Eye and scatter plots
5、 for 4-PSK and 16-QAM fixed links with interference and noise. 23 2 Rep. ITU-R SM.2022-1 Page 5 Summary and conclusions 31 5.1 Improvement obtained in frequency assignment and planning by interference limited environment relative to noise limited environment 31 5.1.1 Wanted fixed link of 4-PSK modul
6、ation format 31 5.1.2 Wanted fixed link of 16-QAM modulation format 31 5.1.3 Wanted fixed link of FSK modulation format. 31 PART B Measurements Page 1 Introduction 32 2 An introduction to available detectors 33 2.1 Characteristics of the International Special Commitee on Radio Interference (CISPR) q
7、uasi-peak (QP) detector 33 2.2 Characteristics of other detectors 33 2.3 Amplitude probability distribution (APD) 34 3 Digital communication services . 35 3.1 General 35 3.2 System characteristics. 35 4 Weighting of disturbance to digital communication systems. 35 4.1 Measurement principle . 35 4.2
8、Interference signals. 36 4.3 Experimental example 1: digital video broadcasting (DVB-C) . 37 4.4 Experimental example 2: digital audio broadcasting (DAB) . 38 5 Conclusion 39 References and Bibliography. 40 Rep. ITU-R SM.2022-1 3 PART C Simulation method for identification of interference source Pag
9、e 1 Introduction 40 2 Simulation method 40 2.1 Simulation set-up 41 2.2 BER calculation using improved importance sampling (IIS) method 42 3 Simulation results . 42 3.1 BER performance . 42 3.2 Probability density of Eb/N050 4 Conclusions 56 PART A Theoretical investigation 1 Introduction This Part
10、A considers the situation where a digital fixed link receives interference from radio (natural) noise plus an unwanted interferer of power set at 6 dB above the natural noise. Current fixed link assignment strategies are commonly noise limited. This means that the minimum receiver signal level under
11、 fading is set to a particular level with respect to the system noise floor and the ambient noise. The assignments are then planned such that the maximum level of an unwanted signal is set by a protection ratio that results in the unwanted signals typically being approximately 6 dB below the noise.
12、This approach is relatively safe and easy to define, but suffers from being sub-optimum. It is advantageous in maximizing the number of links that can be accommodated in a given band and geographical area to arrange that systems are interference limited. In other words, that the unwanted signals, no
13、t natural noise, set the environmental noise floor. Such a strategy brings forth the need to assess the performance of fixed-link receivers in the presence of unwanted signals of other modulation schemes as well as Gaussian noise. This study to considered three types of digital fixed link modulation
14、 schemes of frequency-shift keying (FSK), 4-level phase-shift keying (4-PSK) and 16-level quadrature amplitude modulation (16-QAM) affected by noise and interference from one source of dissimilar modulation scheme, FSK, 4-PSK 8-PSK and 16-QAM. The theoretical investigation was carried out using the
15、signal processing work system (SPW). 4 Rep. ITU-R SM.2022-1 The Report concludes, through analysis of results of computer simulations, that planning and assignment of fixed-links in an interference limited environment (i.e., interference 6 dB above noise) will provide closer physical packing of fixe
16、d-link assignments with increased efficiency. 2 Project work objectives and plan It was intention of this project work to carry out theoretical study according to the agreed objectives and work plan with the sponsor, but additional work was added during the investigative study. 2.1 Project work obje
17、ctives The objective of the study was to simulate the effect on a typical microwave link of unwanted energy consists of both noise and interference (of other modulation schemes) with their signal levels in a defined proportion. Then through analysis assess the potential of spectrum planning and assi
18、gnment strategies based on interference limited scenarios that are more likely to be more efficient. For the purpose of this project work a symbol error ratio (SER), or a bit error ratio (BER), was measured/calculated for a various values of signal to (noise + interference) ratios, S/(N + I), where
19、noise = additive white Gaussian noise (AWGN) and interference = other specified modulation schemes. In all cases, unless specified, the interference level was chosen to be 6 dB above the noise. 2.2 Project work test plan Table 1 lists the tasks that were to meet the specified objectives in 2.1. TABL
20、E 1 Agreed project test cases Task No. Wanted fixed link modulation scheme of Noise and unwanted fixed link type with their signal levels in varying proportions 1 4-PSK modulation format Noise (AWGN) to SER 1 106 2 4-PSK modulation format Noise + 4-PSK interference level 6 dB above the level of nois
21、e 3 4-PSK modulation format Noise + 16-QAM interference level 6 dB above the level of noise 4 4-PSK modulation format Noise + FSK interference level 6 dB above the level of noise 5 16-QAM modulation format Noise (AWGN) to SER 1 106 6 16-QAM modulation format Noise + 4-PSK interference level 6 dB abo
22、ve the level of noise 7 16-QAM modulation format Noise + 6-QAM interference level 6 dB above the noise 8 16-QAM modulation format Noise + FSK interference level 6 dB above the level of noise 9 FSK modulation format Noise (AWGN) to SER 1 10610 FSK modulation format Noise + FSK interference level = le
23、vel of noise 11 Noise + FSK interference level 6 dB above the level of noise 12 Noise + 4-PSK interference level 6 dB above the level of noise 13 Noise + 8-PSK interference level 6 dB above the level of noise 14 Noise + 16-QAM interference level 6 dB above the level of noise Rep. ITU-R SM.2022-1 5 2
24、.3 Additional project work developed during the project During the project work, it became necessary to know two things. One is how wanted fixed links of 4-PSK, 16-QAM and FSK modulation formats are affected by unwanted fixed link of FSK modulation format with its varying modulation index. The other
25、, is how wanted fixed-link of FSK modulation format is affected by unwanted fixed-links of FSK, 4-PSK and 16-QAM formats whilst the wanted FSK fixed-links modulation index is varied. TABLE 2 Additional project work 3 SPW simulation methodology The objective of the project work is to compare, the eff
26、ect on symbol, or bit, error probability of pure Gaussian noise (as reference) and interfering signal plus noise for a variety of test cases specified in Tables 1 and 2. The chosen methodology was to generate SPW simulation designs for a typical fixed-link employing 4-PSK, 16-QAM and FSK modulation
27、formats respectively, validate each design against expected theoretical results and then proceed with simulation for the specified test cases. Subsequent paragraphs give details of simulation design set up, error counting method, justification for its validity and results of required computer simula
28、tions for fixed-links of 4-PSK, 16-QAM and FSK modulation format with their power spectrum density (PSD) plots. Scatter and eye diagrams for wanted fixed-links of 4-PSK and 16-QAM modulation formats with interference signal and noise varied in proportions are also given. 3.1 SPW simulation set up an
29、d designs A typical fixed link simulation design set up consists of wanted signal and an interference signal of required modulation formats that combined into the receiver with a facility to add and vary AWGN to wanted signal to give required signal-to-noise ratio, S/N, or S/(N + I), at the input of
30、 a demodulator, for calculations, or measurements, of BER and SER. Figure 1 shows a generic simulation set up for 4-PSK and 16-QAM wanted fixed-links that consist of a transmitter (Tx), a receiver (Rx) and interference source (Ix). Figure 2 shows the simulation set up FSK wanted fixed-link. Task No.
31、 Wanted fixed link modulation scheme of Noise and Unwanted FSK fixed link modulation index varying from 0.0 to 1 1 FSK modulation format Noise + FSK interference of at a fixed S/(N + I) ratio of 8 dB with the interference level 6 dB above the noise 2 4-PSK modulation format Noise + FSK interference
32、at a fixed S/(N + I) ratio of 15 dB with the interference level 6 dB above the noise 3 16-QAM modulation format Noise + FSK interference at a fixed S/(N + I) ratio of 15 dB with the interference level 6 dB above the noise6 Rep. ITU-R SM.2022-1 3.1.1 SPW design wanted fixed link of 4-PSK modulation f
33、ormat with a receiver A wanted fixed-link employing 4-PSK modulation scheme consists of a transmitter and receiver. For simplicity, Fig. 3 shows SPW design of 4-PSK transmitter and Fig. 4 shows the design of 4-PSK receiver. Rap 2022-01RFamplifierRFmodulatorRRCfilter4-PSK/16-QAMdemodulatorSERmeterRFa
34、mplifierRFmodulatorRRCfilterRFamplifierRFmodulatorRRCfilterInterferencesignal (Tx)4-PSK/16-QAM/FSKWantedsignal (Tx)4-PSK/16-QAMOscillatorTxOscillatorIxAdjustunwantedsignal (Ix) levelfor S/(N + I)*AWGNfor C/N*+To SERmeterFIGURE 1Generic simulation set up for wanted fixed links of 4-PSK and 16-QAMmodu
35、lation schemes with noise and interferenceRRC: root-raised cosine filterRep. ITU-R SM.2022-1 7 Rap 2022-02RFamplifierRF filter6-polerFMdiscrimi-natorDecisionBER meterRFamplifierFSKmodulatorRF filter6-polerRFamplifierRFmodulatorRRCfilterInterferencesignal (Tx)4-PSK/16-QAMTransmitter (Tx)baseband sour
36、ceOscillatorTxOscillatorIxAdjustunwantedsignal (Ix) levelfor S/(N + I)*AWGNfor C/N*+To BERmeterFIGURE 2Simplified simulation set up for wanted fixed links of FSK modulation schemeswith noise and interferenceRap 2022-03Non-linearamplifierFIGURE 34-PSK transmitterComplextime domainfilter4-PSKsourceCom
37、plextoreal/imageSignalgeneratorSignalgeneratorPADWanted 4-PSK source Wanted signal modulator Tx amplifier8 Rep. ITU-R SM.2022-1 Rap 2022-04Non-linearamplifierFIGURE 44-PSK receiverComplextime domainraised cosinefilter4-PSKdemod.MakecomplexSignalgeneratorSignalgeneratorPADCDemodulated 4-PSK signalRec
38、eiver demodulatorRx amplifier4-PSK transmitter: The 4-PSK transmitter is comprised of a 4-PSK source, a RRC, a radio frequency (RF) modulator and an RF amplifier. The output of the amplifier is then combined into the receiver with unwanted interference of similar and other modulation formats and AWG
39、N. The Figures given in Part B show how unwanted interference and AWGN are combined. The same 4-PSK transmitter design was also used to generate 4-PSK and 8-PSK unwanted signals. 4-PSK transmitter simulation parameters: During each SPW simulation the following parameters were set: a) 4-PSK source sy
40、mbol rate: 1.024 Msymbols/s. b) RRC filter: roll-off factor of 0.5 (512 number of delay-taps used to achieve the specified roll-off factor). c) RF modulator: 2.5 MHz. d) RF amplifier: Operating at 10 dB below 1 dB compression point; 3rd order intercept point is set at 6 dB above 1 dB compression poi
41、nt value; 2nd order intercept point set at 16 dB above 1 dB compression point value; RF amplifiers noise figure of 10 dB. 4-PSK receiver: The 4-PSK receiver is consisted of an RF amplifier, RF demodulator, RRC filter with roll-off factor of 0.5 and 4-PSK coherent demodulator. The RF amplifier was se
42、t to operate linearly and the RF demodulator down converts 2.5 MHz carrier, and the 4-PSK demodulator is of matched filter type. The output of the 4-PSK demodulator is fed into the SER counter. 3.1.2 SPW design wanted fixed link of 16-QAM-modulation format with a receiver A wanted fixed-link employi
43、ng a 16-QAM-modulation scheme consists of a transmitter and receiver. For simplicity, Fig. 5 shows SPW design of 16-QAM transmitter and Fig. 6 shows the design of 16-QAM receiver. Rep. ITU-R SM.2022-1 9 16-QAM transmitter: The transmitter is comprised of a 16-QAM source, a RRC filter, an RF modulato
44、r and an RF amplifier. The output of amplifier is then combined into the receiver with unwanted interference of similar and other modulation formats and AWGN. The Figures given in Part B show how unwanted interference and AWGN are combined. The same 16-QAM-transmitter design was also used to generat
45、e unwanted signal. Rap 2022-05Non-linearamplifierFIGURE 516-QAM transmitterComplextime domainraised cosinefilter16-QAMsourceComplextoreal/imageSignalgeneratorSignalgeneratorPADUnwanted 16-QAM source Wanted signal modulator Tx amplifier16-QAM transmitter simulation parameters: During each SPW simulat
46、ion the following parameters were set: a) 16-QAM-source symbol rate: 1.024 Msymbols/s. b) RRC filter: roll-off factor of 0.5 (512 number of delay-taps used to achieve the specified roll-off factor). c) RF modulator: 2.5 MHz. d) RF amplifier: operating at 10 dB below 1 dB compression point; 3rd order
47、 intercept point is set at 6 dB above 1 dB compression point value; 2nd order intercept point set at 16 dB above 1 dB compression point value; amplifiers noise figure of 10 dB. 16-QAM receiver: The receiver is consisted of an RF amplifier, RF demodulator, RRC filter with roll-off factor of 0.5 and a
48、n adaptive equalization with 16-QAM demodulator. The RF amplifier was set to operate linearly and the RF demodulator down converts 2.5 MHz carrier filter type. The output of the demodulator is fed into the SER counter. 10 Rep. ITU-R SM.2022-1 Rap 2022-06Non-linearamplifierFIGURE 616-QAM receiverComp
49、lextimedomainraised cosinefilterFSequalizerMakecomplexSignalgeneratorSignalgeneratorPADCDemodulation of the 16-QAMsignal with the adaptive equalizationReceiver demodulatorRx amplifierIt was necessary to use an adaptive equalization in the demodulation process because the RRC filter caused significant amplitude and phase distortion to the 16-QAM wanted signal. 3.1.3 SPW designs of FSK modulation format with a receiver A wanted fixed-link employing an FSK modulation scheme consists of a transmitter and a receiver. For simplicity, Fig. 7 shows SPW design of FSK tra
