PCMA (Paired Carrier Multiple Access) - a patented ViaSat technology - is a fundamentally new technique for two-way satellite communications. PCMA is a novel method for frequency re-use with existing and planned satellites which allows two different earth stations to use the same frequency, time slots, and/or CDMA code at the same time.
This technique can be applied with any of the commonly used multiple access techniques such as FDMA, TDMA, or CDMA. PCMA may also be applied independently of the modulation and coding technique for the link. PCMA is used in addition to -- not instead of -- other bandwidth and power efficient modulation, coding and multiple access techniques.The benefit of PCMA is that it may effectively double the throughput of satellite systems in terms of bits/sec/Hz, with a minimal impact on the Eb/No required to achieve a desired Bit Error Rate.
ViaSat has implemented PCMA in our StarWire Calypso and Aurora terminals at 8kbps and 16kbps OQPSK. As part of the development process, ViaSat has performed extensive performance testing both at IF, RF and over-the-air. The figures at left and below show the Bit Error Rate (BER) performance vs. signal to noise ratio of the Aurora modem running PCMA with Rate = 1/2 and Rate = 3/4 convolutional coding. Each figure provides several curves: theoretical coded performance, theoretical uncoded performance, modem performance without PCMA, and modem performance with PCMA at 0 dB and 10 dB Near/Far ratios.
The Near/Far ratio is the ratio of receive Near signal power (undesired signal from local modem to be canceled) to the Far signal power (desired signal from remote terminal). These curves reflect PCMA performance test data taken at IF and RF. IF testing was performed with back to back modems at a 70 MHz IF. RF testing was performed using a C-Band radio and a satellite test translator with SSPA operating points suitable for multi-carrier operation (up to 3 dB backoff from saturation).
Properly applied, PCMA can be a powerful tool to double the capacity of emerging satellite systems offering fixed site services ranging from basic telephony to high speed Internet access. The technology underlying PCMA has been granted a US patent.
White Paper
To view the white paper, please go to our Technical Library.