A communication system based on an ultraviolet (UV) laser at 266 nm is presented to improve the communication distance. The pulse frequency-shift keying (FSK) modulation scheme is studied and improved in order to reduce the bit error rate (BER), and is put into practice on a field programmable gate array (FPGA). The mathematical models of the modulation and demodulation are established. A test platform is set up to measure the energy density and pulse response under different distances and receiver elevation angles. It is shown that the omnibearing communication can be realized, and the bit rate is limited to 12.5 Mbit/s. The BER is estimated to be less than 10 -7 at distance of 300 m in line-of-sight (LOS) communication model and to be less than 10 -6 at distance of 80 m in non-line-of-sight (NLOS) communication model. Ultraviolet (UV) communication has become an interesting alternative for military communications in the last two decades. In the UV band (200-280 nm), because the sunlight is filtered by the ozone layer and the background radiation is low, weak signals can be detected by the receiver. Meanwhile, the UV light can propagate for only several kilometers due to the high atmospheric scattering and absorption, so the hostile forces cannot detect the signal on our part. UV communication becomes an important military application when radio, wire or fiber communication links are unavailable, unreliable or untrustworthy. It has attracted the attention of researchers because of its good secrecy in recent years. A scattering communication link at ultraviolet frequencies was put forward by Sunstein [1] in 1968. A single scattering channel model for non-line-of-sight (NLOS) was proposed by Luettgen et al [2] in 1991, and became an authoritative cited reference [3][4][5][6] . The experimental performance using this model was studied for pulse-position modulation (PPM) or on-off keying (OOK)modulation on light emitting diode (LED) based test bed [5,7,8] . However, the communication distance is restricted to dozens of meters because the light output power of LED is finite.In this paper, a pulse laser is utilized as the UV source to increase the communication distance. The mathematical models of modulation and demodulation are established. The binary frequency-shift keying (2FSK) is applied and improved to adjust the laser device, and a modified quaternary frequency-shift keying (4FSK) is imported for comparison. A statistic bit error rate (BER) is conducted to explain the performance of the communication system. The UV communication system consists of two basic components: the transmitter (Tx) and the receiver (Rx) [9] . In the transmitter, a pulse laser is modulated by a field programmable gate array (FPGA) to carry digital signal generated from a computer. The output UV light is scattered through atmosphere channel to establish a communication link. At the receiver, a photomultiplier tube (PMT) aided by a solar-blind optical filter is employed for light detection, and another FPGA is utilized to demodulate the si...