Optimization of pilot Locations in Adaptive M-PSK Modulation in a Rayleigh Fading Channel Khaled Almustafa Information System Prince Sultan University

Presentation Outline Introduction What is Modulation? Spectral Efficiency Adaptive Communication Channel Model Adaptive M-PSK Modulation Threshold Optimization Assumptions Numerical Simulation Future Work

Introduction The radio spectrum available for wireless services is limited. Hence, Spectral efficiency is of highest concern in the design of future wireless data communications system. Such efficiency can be improved with the use of adaptive techniques.

Continue….. Introduction A better utilization of the channel capacity can be done by adapting the parameters of the transmitted signal to the state of the channel fading in term of average SNR, which is given, for the case of Perfect CSI by: and are the channel and the noise variance, and is the energy of the transmitted data.

What is Modulation? Modulation is the process of varying a characteristic of a wave by the characteristic of another wave. We have two basic type of modulation: Analog modulation and Digital modulation.

Digital Modulation There are three basic types of digital modulation techniques: – Amplitude-Shift Keying (ASK) – Frequency-Shift Keying (FSK) – Phase-Shift Keying (PSK)

PSK Modulation It is modulation of data achieved by changing the phase of the modulated signal depending on the modulating signal. E.g. BPSK: modulating signal (message) 1 or 0 modulated signal (carrier) 1  psase =0 0  phase=180

M-PSK Modulation (b)(a)(c)(d) Figure 1

Spectral Efficiency The Spectral Efficiency of M-PSK Modulation can be approximated by – Where R is data rate, W is the Channel bandwidth and M is the constellation size used.

Modulator Constellation Size Selector Demodulator Rayleigh Channel Input Data Transmitter Output Data Feedback Path Receiver Adaptive Communication System Model

Adaptive M-PSK Modulation Adaptive Scheme – Bad channel measurement, in term of SNR, we have small constellation size, BPSK – Good channel measurement, we have bigger constellation size Q-PSK, 8-PSK, up to 64-PSK. We have to divide range of the channel SNR into number of regions in order to choose the required constellation size based on the region.

Threshold optimization After specifying threshold level, dividing the range of the channel SNR into regions. We calculate the value of constellation size for each SNR values for specific BER 0.

Continue …. Threshold optimization In order to use adaptive modulation, a decision rule has to be developed based on a predicted SNR. We can derive a desired SNR threshold for a given target BER.

Structure of the Transmission Scheme

Assumptions  Knowledge of the channel measurement is send to the transmitter through a reliable-error free feedback from the receiver.  The receiver has the ability to measure the effective SNR of the channel at each time of the transmission, and has full knowledge of the channel.

Numerical Simulation For different targeted BER For different pilot location Investigate the limited feedback.

Numerical Results:

Future Work Joint distribution of SNR estimates obtained at the transmitter and the receiver. Find an analytical formula for BER with the limited feedback approach. Apply the modulated scheme into a Mobile to Mobile environment.