This paper focuses on several design issues of coherent optical wireless systems as a means of providing high data rate optical links in indoor environments enabling the realization of ultra-broadband wireless local area networks. We show how the performance specifications can be translated into signal-to-noise ratio requirements inside the coverage area, taking into account the laser phase noise mitigation scheme. We then discuss the power budget details using Gaussian beam optics incorporating the transceiver positioning and the optical systems used at the transmitter and receiver side. We also treat the influence of ambient light noise. We show that coherent optical wireless systems are characterized by excellent signal-to-noise performance enabling networking at very high data rates. Our results indicate that 2 Gb/s and 10 Gb/s data rates can be easily sustained at 3 m distances over a circular coverage area of 1 m radius using Class-1 lasers for the transmitter and the local oscillator. We also discuss the power gain compared to intensity modulated/direct detection optical wireless and show that it can be as high as 20 dB, especially near the edge of the coverage area.