The engineer designing a broadband wireless Internet access link is tasked with developing a system that insures reliable data delivery at high data rates and low cost. At the core of the data integrity issue is the ability to detect and correct errors in the transmitted data stream. AHA's Turbo Product Codes technology offers significant performance gains over all other error correction technologies available in silicon today. This increased performance allows the system designer to increase the data rate, reduce antenna size, reduce broadcast power, and/or extend the range of the transmission link. Turbo Product Codes offer flexibility in code performance that can adapt on the fly to the changing transmission channel of the wireless world, as well as support the wide range of packet sizes of Internet traffic.
The gain afforded by TPCs over more traditional FEC methods such as Reed-Solomon (RS) and Reed-Solomon/Viterbi (RSV) coding substantially is typically 3 to 4 dB of Eb/No performance. This puts TPCs within 1.5 dB of the Shannon capacity. A 3 dB performance gain can mean a reduction in antenna diameter by 30 percent, a decrease in transmission power, a transmission distance increased by 40 percent, or increased data throughput.
In the transmitter, TPCs are placed in the data path between the source data and the modulator as shown in Figure 1. The source data to be transmitted is encoded by the TPC encoder and the Error Correction Code (ECC) bits are added to each block. The encoded output data is mapped according to the modulation used (i.e., QPSK, QAM). The modulated output is transmitted over the wireless link. At the receiver, the channel data is first demodulated and then mapped into soft metrics (soft confidence values for the received symbols). The TPC decoder inputs the soft metrics and computes the decoded data values. The ECC bits are automatically removed from the data stream.
Figure 1: TPC in System
New TPC devices such as the AHA4540B device support full duplex encoding and decoding as well as supporting such system operations as symbol mapping, synchronization and framing. The AHA4540 device can operate at data rates up to 155 Mbits/sec facilitating its use in even the highest performing wireless data link.