I. INTRODUCTION

II. CURRENT CHANNEL ACCESS METHODS

III. NON-ORTHOGONAL MULTIPLE ACCESS

IV. GRANT-FREE ACCESS FOR M MTC

V. GRANT-FREE NOMA SCHEMES

VI. MACHINE LEARNING IN GRANT-FREE NOMA

VII. INFORMATION THEORETIC PERSPECTIVE OF GRANT-FREE NOMA

VIII. PRACTICAL CHALLENGES AND SOLUTIONS FOR GRANT-FREE UL NOMA

X. CONCLUSION