System Generator Based Implementation of QAM and Its Variants Nilesh Katekar *1, Prof. G. R. Rahate*2 *1 Student of M.E. VLSI & Embedded system, PCCOE Pune, Pune University, India *2 Astt. Prof. in Electronics and Telecommunication department, PCCOE Pune, Pune University, India *1 nileshkatekar05@gmail.com, *2 ganesh.rahate@pccoepune.org Abstract: Quadrature amplitude modulation (QAM) is widely used modulation technique in today s wireless communication system. As it support the high data rate transmission and it efficiently uses the power and bandwidth resources. In this paper, basic QAM and its two variants are implemented in Xilinx system generator and output is observed and analyzed Keywords: QAM, BER, system generator I Introduction QAM is combinations of two modulation technique ASK and PSK, as it gives the variation in both amplitude and phase at the output. QAM has the ability to transmit the high data rate due to that it is widely used modulation technique in wireless technologies like 3G, Wi-Fi, Wi-MAX etc. However, it must also be noted that when using modulation technique such as 64 QAM, better signal-to-noise ratios (SNRs) are needed to overcome any interference and maintain a certain bit error ratio (BER) [1] Use of different QAM variants at different time is depends on the channel condition. When channel condition is good or user equipment is near to the transmission station then higher order modulation is preferred such as 64 QAM, and when channel condition is poorer then lower order modulation technique has to be switched such that 64 QAM to 16 QAM or 8 QAM as per the required BER. This is adaptive modulation technique used in today s wireless technology. II Related Work Reference [4] is a text book; it explores the basics of QAM and modulation techniques with help of diagrams, waveforms and mathematical equations. In reference [2] author has implemented the simulink based QAM system using the direct simulink block sets and plotted the result on error rate versus SNR(db). In reference [7], author s implemented16 QAM modulation and demodulation in MATLAB, calculated results for different BER for different SNR values and compare the 16 QAM BER results with BPSK and QPSK modulations and concluded that performance of 16 QAM modulations is superior to BPSK and QPSK modulation. In reference [8], authors implemented the 16 QAM transmitter and receiver on FPGA. In this paper authors design 16 QAM modulator and demodulator in MATLAB system generator and obtain the results on FPGA board. In paper [1] author implemented QAM modems on FPGA using partial reconfiguration and as per the user requirement, user can switch between different modulations and demodulations technique in runtime by configuring control register in FPGA, switching between different modulations manually. Here authors of this paper are trying to make system adaptive by passing different channel conditions and a partial work in this direction is presented in this paper. III Basics of QAM Among all the forms of digital modulation used in communication system QAM is different. In this system, digital signal to be transmitted is acts both on amplitude and as on the phase of the carrier signal. Therefore, QAM modulation is a mix of ASK with PSK[4] Fig 1: Construction of QAM [3]
Figure 1 shows, QAM is combinations of both ASK and PSK modulation scheme. In the output of QAM both variation can observe. Figure 2 shows the QAM modulator. In this, two message signals are applied to the separate product modulator with same carrier frequency with 90 degree phase. The signal S(t) consist of the sum of these two product modulator outputs as shown by[6] Figure 4 shows the constellation diagram of QAM and its variants. In QAM as the order of QAM increases then data transmission rate also increases. S(t) = AcM 1(t)cos(2πfct)+AcM 2(t) sin(2πfct) --(1) Where M 1 (t) and M 2 (t) are the two different message signal applied to product modulator. Fig 2: QAM modulator [4] Figure 3 shows the QAM demodulator. In this transmitted combine signal are separated and the transmitted data is recovered. The multiplexed signal S(t) is applied simultaneously to two separate coherent detectors that are supplied with two local carrier of the same frequency but differing in phase by -90 degree Fig 4: Constellation diagram of different QAM variants [6] IV Implementation QAM modulator In this section, implementation QAM modulator in system generator is given. Figure 5 shows the basic QAM modulator implementation. In modulator, digital input bits are divided in to two parts using the time division demultiplexer (TDD) block. The one output of TDD is given to Inphase modulator and other is given to quadrature phase modulator. Carrier frequency provided to both modulators is of same frequency with 90 degree phase shift. Fig 3: QAM Demodulator [4]. The output of top detector is AcM 1(t), whereas the output of the bottom detector is AcM 2(t)[4] Fig 5: QAM Modulator Implementation In QAM modulator output, phase and amplitude is varies in accordance with the modulating signal. Parameter setting for system generator block is given table 1. Sr. Block Parameter
1 LFSR Bits in LFSR = 8, F/B polynomial 11, initial value C6 2 TDD Frame sampling pattern [11] 3 DDS Output selection sine and cosine, explicit period 1/3000, output freq 0.3Mhz Table 1: Parameter setting for QAM modulator Waveform 3 Waveform 4 Fig 6.1: QAM Implementation output (fig 1. Input bit signal, fig 2 & 3 first and second modulator output, fig 3: output of QAM) Fig 7: 8 QAM modulator implementation Figure 8.1 shows the waveform for 8 QAM modulator implementation, digital data and final output is shown waveform 1 and waveform 2 respectively. In fig 8.2 amplitude variation and phase change is shown by zoom in the waveforms. Sr. Block Parameter 1 LFSR Bits in LFSR = 24, F/B polynomial 11, initial value 0B42FE 2 TDD Frame sampling pattern [1 1 1] 3 DDS0 Output selection sine, explicit period 1/5000, output freq 0.5Mhz 4 DDS1 Output selection sine(with tick negative sine) rest same as DDSO 5 DDS2 Output selection cosine, rest same as DDS0 Table 2: Parameter setting for 8 QAM modulator implementation Fig 6.2: Zoom in output of basic QAM (: input bit, waveform 2: output of QAM) V Implementation of 8 QAM modulator In 8 QAM, TDD is used of single input to 3 bit divider. Carrier source is provided of same frequency with different phase and sign. Figure 7 shows the block wise implementation of 8 QAM. Fig 8.1: 8 QAM modulator output (: input bit signal, waveform 2: output of 8 QAM )
4 DDS1 Output selection cosine rest same as DDSO 5 DDS2 Output selection sine(with tick negative sine), rest same as DDS0 6 DDS3 Output selection cosine (with tick negative cosine), rest same as DDS0 Table 3: Parameter setting for 16 QAM modulator implementation Fig 8.2: Zoom in output of 8.1waveform In fig 8.2 shows that the amplitude and phase change in the output waveform of 8 QAM. V Implementation of 16 QAM Modulator Figure 9 shows the 16 QAM modulator implementation, in that TDD is use of 1 to 4 demultiplexer type and that provide four different modulator with four different carriers which of same frequency but different in phase and sign. Waveform 3 Waveform 4 Fig 10.1: 16 QAM modulator output (waveform 1 is Input bit signal, waveform 2 & 3 First and second Adder output, waveform 4 is output of QAM third adder output) Fig 9: 16 QAM modulator Implementation Sr. Block Parameter 1 LFSR Bits in LFSR = 24, F/B polynomial 11, initial value 0B42FE 2 TDD Frame sampling pattern [1 1 1 1] 3 DDS0 Output selection sine, explicit period 1/5000, output freq 0.2Mhz Fig 10.2: Zoom in input output of 16 QAM VI Future scope Implementation of QAM and its variants as adaptive modulation on FPGA and applying partial reconfiguration to this to reduce power and size of design.
VII Conclusion In this paper, different QAM modulators are designed in Xilinx system generator and required results are simulated and validated.. VI References: [1] Arun Kumar K A, FPGA Implementation of QAM Modems Using PR or Reconfigurable Wireless Radios, International Conference on Microelectronics, Communication and Renewable Energy (ICMiCR-2013) [2] Xiaolong Li, Simulink-based Simulation of Quadrature Amplitude Modulation (QAM) System [3] Mr.Gaurang Rajan, Prof. Kiran Trivedi Prof.R.M.Soni, design and implementation of 4- QAM Architecture for OFDM communication system in VHDL using Xilinx, ISSN: 0975 6779 NOV 12 TO OCT 13 VOLUME 02, ISSUE 02. [4] Simon Haykin, Communication System, Fourth Edition" [5] E. J. McDonald, The aerospace corporation Los Angeles, Runtime FPGA partial reconfiguration, IEEEAC paper#1443 [6] www.radio-electronics.com [7] Tan Mingxin, Zhang Lanlan, Shuren He, The implementation of 16QAM modulation and demodulation and performance comparison, IEEE 2009 [8] Raghunandan swain, Ajit Kumar Panda, Design of 16-QAM transmitter and receiver: review of methods of implementation in FPGA, International Journal of Engineering and Science, ISSN: 2278-4721, Vol. 1, Issue 9 (November 2012),