While bandwidth in terrestrial networks continues to explode exponentially, satellite communications systems are more limited in growth due to the high cost of deployment. As a result, the bandwidth of the satellite link is a most cherished commodity. The engineer developing a satellite communications system is under great pressure to design the most efficient channel for data communications possible.
At the core of the channel efficiency issue is the desire to transmit the greatest amount of data in the most reliable manner. By using the most advanced error detection and correction technology available, the communications channel can achieve near optimum performance. AHA's Turbo Product Codes technology fills this requirement offering significant performance gains over all other error correction technologies available in silicon today. TPCs are becoming the preferred error correction solution for satellite networks because of their performance advantage and flexibility.
Fig. 1: VSAT Block Diagram
Turbo Product Codes (TPCs) offer a wide range of flexibility in code rate and packet size to adapt to the changing transmission channel of the satellite link. Because the TPC coding can be changed on a block by block basis they are especially well suited for variable data packet sizes such as Internet traffic.
TPCs typically outperform the Digital Video Broadcasting (DVB) standard Reed Solomon Viterbi coding solution by 1.5 dB or more. This puts TPCs as close as 1 dB to the Shannon Capacity.
Some example 4K block TPC codes commonly used in satellite links are listed below. The Eb/No performance at a BER of 10^-8 is also listed for BPSK modulation over an AWGN channel. These results are all from hardware measurements using the AHA4501 TPC device.
Fig. 2: 4K Block TPC Codes Commonly Used in Satellite Links
| Code Configuration | Block Size | Data Size | Code Rate | EB/No at 10^-8 |
|---|---|---|---|---|
| (64,57)x(64,57) | 4096 | 3249 | .793 | 3.6 dB |
| (32,26)x(32,26)x(4,3) | 4096 | 2028 | .495 | 2.4 dB |
| (16,11)x(16,11)x(16,11) | 4096 | 1331 | .325 | 1.9 dB |
Figure 3: BER vs Eb/No performance of typical TPC codes used in satellite modems
New TPC devices such as the AHA4540B and AHA4501 are ideal for incorporation into a satellite link. The AHA4540 supports full duplex encoding and decoding as well as supporting such system operations as symbol mapping, synchronization and framing. It operates at data rates up to 155 Mbits/sec facilitating its use in even the highest performing wireless data link.