Modular Arithmetic CPM for SDR Platforms

This brief presents a new Continuous Phase Modulation (CPM) module for multi- $h$ transmission based on modular arithmetic processing. It is well known that CPM systems are sensitive to changes in the modulation index, which is implied when fixed-point format is used in the hardware implementation. In this scenario, modular arithmetic allows a more accurate signal processing regarding SQNR performance. This proposal has been shown to improve performance compared to other state-of-the-art methods, even when the modulation indices do not have an exact representation in a given fixed-point format. Due to its highly reconfigurable architecture, this hardware block is suitable for Software Defined Radio (SDR) platforms. A complete digital architecture is also provided. Implementation results show that the new proposal have clear advantages in terms of hardware resources and operating frequency against other CPM transmitters in open-literature.

I. Introduction

Continuous phase modulation (CPM) is a digital modulation format that keeps a constant envelope while presenting high spectral efficiency by smoothing the phase transitions [1]. The interest and efficiency of CPM techniques has been confirmed by industrial communications standards. For example, Bluetooth uses GFSK [2], MILSTD-188-181B for voice-over-satellite communications [3] uses dual-h CPM and IRIG-106-15 for aeronautical telemetry [4] employs SOQPSK-TG. More recently, CPM has emerged as an alternative modulation scheme for resolving problems in GPS codes [5], [6] and for future satellite broadcasting [7]–[9].