Part I Introduction. 1. INTRODUCTION. 1.1 A Brief History of Wireless Optical Communications. 1.2 Overview. 2. WIRELESS OPTICAL INTENSITY CHANNELS. 2.1 Wireless Optical Intensity Channels. 2.2 Optoelectronic Components. 2.3 Noise. 2.4 Channel Topologies. 2.5 Summary. 3. AN INTRODUCTION TO OPTICAL INTENSITY SIGNALLING. 3.1 Communication System Model. 3.2 Bandwidth. 3.3 Example Modulation. 3.4 The Communication System Design Problem. Part II Signalling Design. 4. OPTICAL INTENSITY SIGNAL SPACE MODEL. 4.1 Signal Space of Optical Intensity Signals. 4.2 Examples. 4.3 Conclusions. 5. LATTICE CODES. 5.1 Definition of Lattice Codes. 5.2 Constellation Figure of Merit, Gain. 5.3 Baseline Constellation. 5.4 Spectral Considerations. 5.5 Gain versus a Baseline Constellation. 5.6 Continuous Approximation to Optical Power Gain. 5.7 Coding Gain. 5.8 Shaping Gain. 5.9 Shaping Gain: Expression. 5.10 Shaping Gain: Peak-Symmetric Schemes. 5.11 Opportunistic Secondary Channels. 5.12 Example Lattice Codes. 5.13 Conclusions. 6. CHANNEL CAPACITY. 6.1 Background. 6.2 Problem Definition. 6.3 Bandwidth Constraint. 6.4 Upper bound on Channel Capacity. 6.5 Lower bound on Channel Capacity. 6.6 Examples and Discussion. 6.7 Conclusions. Part III Multi-Element Techniques. 7. THE MULTIPLE-INPUT / MULTIPLE-OUTPUT WIRELESS OPTICAL CHANNEL. 7.1 Previous Work. 7.2 The MIMO Wireless Optical Channel. 7.3 Design Challenges. 7.4 Pixel-Matched System. 7.5 The Pixelated Wireless Optical Channel. 7.6 Conclusions. 8. PROTOTYPE MIMO OPTICAL CHANNEL: MODELLING & SPATIO-TEMPORAL CODING. 8.1 Experimental Prototype. 8.2 Channel Model. 8.3 Pixel-Matched Systems. 8.4 Pixelated Wireless Optical Channel. 8.5 Conclusions. 9. CONCLUSIONS AND FUTURE DIRECTIONS. 9.1 Conclusions. 9.2 Future Work