QAM and QPSK:
Aim:
Review of Quadrature Amplitude Modulator (QAM) in digital communication system, generation of Quadrature Phase Shift Keyed (QPSK or 4-PSK) signal and demodulation.

Introduction:
The QAM principle: The QAM modulator is of the type shown in Figure 1 below. The two paths to the adder are typically referred to as the ‘I’ (inphase), and ‘Q’ (quadrature), arms.

Not shown in Figure 1 is any bandlimiting. In a practical situation this would be implemented either at message level - at the input to each multiplier - and/or at the output of the adder. Probably both ! The motivation for QAM comes from the fact that a DSBSC signal occupies twice the bandwidth of the message from which it is derived. This is considered wasteful of resources. QAM restores the balance by placing two independent DSBSC, derived from message #1 and message #2, in the same spectrum space as one DSBSC. The bandwidth imbalance is removed. In digital communications this arrangement is popular. It is used because of its bandwidth conserving (and other) properties.

It is not used for multiplexing two independent messages. Given an input binary sequence (message) at the rate of n bit/s, two sequences may be obtained by splitting the bit stream into two paths, each of n/2 bit/s. This is akin to a serial-to-parallel conversion. The two streams become the channel 1 and channel 2 messages of Figure 1. Because of the halved rate the bits in the I and Q paths are stretched to twice the input sequence bit clock period. The two messages are recombined at the receiver, which uses a QAM-type demodulator. The two bit streams would typically be band limited and/or pulse shaped before reaching the modulator. A block diagram of such a system is shown in Figure 2 below.

QAM becomes QPSK: The QAM modulator is so named because, in analog applications, the messages do in fact vary the amplitude of each of the DSBSC signals. In QPSK the same modulator is used, but with binary messages in...

...The design for QAM modulator below is for a standard 16-QAM constellation. The general form of an M-ary signal can be defined as S(t) = sqrt((2*Emin)/Ts)*ai*cos(2πfot) + sqrt((2*Emin)/Ts)*bi*sin(2πfot) Here, Emin is the energy of the signal with lowest amplitude and ai and bi are pair of independent integers chosen according to the location of the particular signal point. Fo is the carrier frequency and Ts is the symbol period. Non-rectangular QAM constellations achieve marginally better bit-error rate (BER) but are harder to modulate and demodulate. Hence, below is the simulation of a rectangular QAM constellation. Simulation model in MATLAB Following is the methodology of simulation of the QAM modulator in MATLAB, 1) Generation of random binary sequence, this is the input which is to be modulated. 2) Assigning group of 4 bits to each 16-QAM constellation symbol per the Gray mapping 3) Addition of white Gaussian Noise 4) Demodulation of 16-QAM symbols Upon reception of the signal, the demodulator examines the received symbol, which may have been corrupted by the channel or the receiver (e.g. additive white Gaussian noise). It selects, as its estimate of what was actually transmitted, that point on the constellation diagram which is closest (in a Euclidean distance sense) to that of the received symbol. Thus it will demodulate incorrectly if the corruption has caused the...

...International Journal of Computer Communication and Information System ( IJCCIS) – Vol2. No1. ISSN: 0976–1349 July – Dec 2010
Hardware Implementation of Viterbi Decoder for Wireless Applications
Bhupendra Singh1, Sanjeev Agarwal2 and Tarun Varma3
1
Deptt. of Electronics and Communication Engineering, Amity School of Engineering and Technology, Noida, India Email: 1bsingh.tech@gmail.com 2,3 Malaviya National Institute of Technology, Jaipur, India Email: 2san@mnit.ac.in, 3tarun.varma.jaipur@gmail.com controlled shift register is designed at the circuit level and integrated into the ACS module. A. Structure of Viterbi Decoder The four functional blocks of VD in term of implementation, including branch metric unit (BMU), add-compare-select unit (ACSU), feedback unit (FBU) and survivor memory unit (SMU).
Abstract—In 2G mobile terminals, the VD consumes approximately one third of the power consumption of a baseband mobile transceiver. Thus, in 3G mobile systems, it is essential to reduce the power consumption of the VD. In this report the register exchange (RE) method, adopting a pointer concept, is used to implement the survivor memory unit (SMU) of the VD. For the implementation part, hardware implementation of MLVD through Synopsys Design Compiler Synthesis is done. For synthesis UMC-180nm Library is used. Index Terms— Viterbi Decoder, SMU, ACSU, RE, MLVD I. INTRODUCTION The register exchange (RE) method, adopting a pointer concept, is used to implement the...

...
Homework 7_1
ECET310
For a QPSK system and the given parameters, determine
Carrier power in dBm
Noise power in dBm
Noise power density in dBm
Energy per bit in dBJ
Carrier-to-noise power ratio
Eb/No ratio
PC=10-12 W,fb=20Kbps
PN=10-16 W,B=60 KHz
10 log (10^-12/.001)=-90dBm
10 log(10^-16/.001)= -130dBm
10 log(pn/.001)- 10logB= NdBm- 10logB = -130dBm-10log(60khz)= -177.8dBm
10 log(pc/fb)= 10 log(10^-12/20kbps)= -163dBj
Pc/pn= 10 log (pc/pn)= 10 log (10^-12/10^-16)= 40dB, 41dB
Eb/No (dB) = 10log(C/N) + 10log(B/fb) = 40+ 10 log(60khz/20kbps)=44.77dB
Which system requires the highest Eb/No ratio for a probability of error of 10-7, four-level QAM or 8-PSK system?
The level 4 QAM system.
Determine the minimum bandwidth required to achieve a P(e) of 10-4 for a 16-PSK system operating at 25 Mbps with a carrier-to-noise ratio of 10 dB.
B / fb = Eb / No – C / N = 18.3 dB – 10 dB = 8.3 dB
Log^-1(8.3/10)=6.76
B= 6.76*25mbps= 169Mbps
A PCM-TDM system multiplexes 32 voice channels each with a bandwidth of 0 Khz to 4 KHz. Each sample is encoded with an 8-bit PCM code. UPNRZ encoding is used. Determine:
The line data rate
(32)(8000)(8)=2.04mbps
Minimum sampling rate
=2(4khz)=8khz
Minimum Nyquist bandwidth
UPnRZ= Fb= 2.04mbps
Consider a PCM-TDM system in which 24 signals are to be processed. Each signal has a baseband bandwidth of 3 KHz. The sampling rate has to be 33.3% higher than the...

...Analysis of
Design and Simulation of QPSK Modulator for Optic Inter Satellite Communication:Review
Submitted by
A Penchala Bindushree
4th Sem, M.Tech (DCE)
Acharya Institute of Technology
Bangalore – 560090
Under the guidance of
Internal Guide:
Nataraju A B M.tech, (PhD)
Assistant Professor, ECE Department
Acharya Institute of Technology
Bangalore – 560090
External Guide:
Vijesh T V
Scientist/Engineer ‘SC’
LEOS/ISRO
Bangalore-560013
Abstract
We have proposed a digitally implemented QPSK system for Free-Space Optics systems for future satellite missions. We have used a Laser source of 1550nm wavelength and data rate of 2.5Gbps.The system consists of a modulating and a demodulating block and an advantage of filters added to improve the performance and optimize errors like noise.
The best suited modulator for FSO is Mach-Zehnder modulator which is tuned for high performance. The LiNB03 demodulator demodulates the signal which in turn passed to a filter to attenuate the demodulated output and then through an amplifier to increase the signal strength. Digital approach for implementation of QPSK Modulation is attempted here and compared with existing systems. Simulation and characterization is done to freeze design parameters. The system mainly concentrates on parameter like performance, security, minimum size and cost saving which will be the future of satellite communications.
1. INTRODUCTION
In...

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