EE310 Integrated Circuits Seminar, 10/15/02

Ann Guerra guerra at par.stanford.edu
Mon Oct 14 22:06:38 PDT 2002


  EE310 Integrated Circuits Technology and Design Seminar

"Design Tradeoffs for Continuous Phase Modulation: Capacity
	  Bounds vs.Linearity and Power Backoff"

			Kevin Yu
		  Stanford University

	       Tuesday, October 15, 2002
			4:15 p.m.
		Building 380, Room 380X


			ABSTRACT

Modern communications demands smaller, cheaper, more portable devices
capable of higher communication rates.  Thus, integration technologies
such as CMOS are very appealing.  Integration, however, requires the
analog transmitter and receiver devices to be designed in CMOS
technology.  Linearity of the final power amplifier is difficult to
achieve with small power budgets.  Furthermore, highly inefficient
power amplifiers imply lower battery lifetimes and larger heat
dissipation.  Traditionally, linear modulation techniques are used due
to their higher capacity.  Furthermore, error correction coding is
well studied for linear modulation techniques.  However, a class of
constant envelope nonlinear modulation techniques exist which are
conducive to implementation in CMOS. However, due to their nonlinear
nature, understanding of coding and even fundamental information
capacity are not well understood.

In this talk, we will discuss the basic ideas of nonlinear modulation
using Continuous Phase Modulation (CPM).  We examine the difficulties
in analysis caused by the nonlinearity of the CPM.  We will derive
upper bounds on the capacity of an additive white Gaussian noise
channel using Continuous Phase Modulation and propose some coding
methods which may achieve near capacity performance.  To derive the
capacity bounds, we propose using an arbitrary number of linear,
filtered pulses to form an MMSE approximation to Laurent's linear
decomposition of arbitrary binary input CPM.  Using this decomposition
and approximation, the capacity bounds in white and colored Gaussian
noise is derived by showing the system is equivalent to a multiple
antenna channel with intersymbol interference (ISI).  The capacity of
such a channel is used as the upper bound.  Furthermore, we use this
decomposition and approximation to derive some design insights for the
power backoff needed in the power amplifier.  Numerical results are
presented for a channel using CPM with both white and colored noise.
The bounds show a significant gap between a channel using CPM and a
channel with unconstrained modulation.







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