Glossary of terms 16-QAM Sixteen-state quadrature amplitude modulation. 16-APSK Sixteen-state amplitude/asymmetric phase shift keying. 29 ­ 25 log 10 Mathematical characteristic describing performance of an SNG uplink antenna to meet the 2° satellite spacing requirement. 2B D Basic rate ISDN, with 2 64 kbps bearers and a 16 kbps data channel. 32-APSK Thirty-two-state amplitude and phase-shift keying or asymmetric phase-shift keying. 3G Third generation digital cellular mobile telephony system. 4:2:0 Describes a picture where the chrominance is sampled at half the rate relative to luminance, in both the horizontal and vertical planes. 4:2:2 Describes a picture where the chrominance is sampled at half the rate relative to luminance in the horizontal plane, but at the same rate as luminance in the vertical plane. 4:4:4 Describes a picture where the chrominance and luminance are sampled at the same rate in both the horizontal and vertical planes: effectively chrominance is given the same bandwidth as the luminance. 601 See ITU-R BT.601. 64-QAM Sixty-four-state quadrature amplitude modulation. 8-PSK Eight-phase-shift key modulation. A Ampere (or amp): measurement of electrical current. AAC Advanced Audio Coding. ABC American Broadcasting Company: US network formed in 1945 from the Blue Network Company, which was originally NBC's Blue Network. AC Alternating current: type of electrical current. AC-3 See Dolby AC-3. ACATS Advisory Committee on Advanced Television Service. Access The general term for the ability of a telecommunications user to make use of a network. Acceleration The process of an uplink station continuously transmitting TCP/IP data packets over a satel- lite link without waiting for the receiving station to send an acknowledgement, to minimize latency. ACM Adaptive Coding and Modulation. ACT-L3 Proprietary video/audio compression system developed by Streambox Inc. (US). ACTS Advanced Communication Technologies and Services (EU project). Ad-hoc capacity Capacity available for bookings on a temporary basis; see Occasional use; capacity. ADC Analog-to-digital conversion: process of converting analog signals to a digital representation. DAC represents the reverse translation. ADPCM Adaptive differential pulse code modulation. Algorithm Refers to the computational code used to compress or decompress a signal. AM Amplitude modulation.