Within the telecommunications industry, data distortions that may occur during transmission of data through various communications channels are a constant source of concern. These data distortions may include, for example, data frame losses, bit errors that occur during transmission, interference from other communication channels or nearby sources of interference, errors introduced by local weather phenomenon or atmospheric distortion and attenuation, antenna misalignment and other errors that may result during transmission. Data distortions during transmission may result in lost or erroneously communicated data. These data distortions limit the effectiveness of data communications, resulting in lower data throughput as transmitted data is lost. There is significant interest in determining channel characteristics for systems where the waveform does not support the use of conventional testing systems such as standard bit rate error testers or packet testers. These waveforms are typically layer one frame-based, comprising a series of fixed or variable length baseband layer one transmission frames, each of which is typically processed independently. Generally, standard bit error rate testers do not typically support measurements of distortions and errors in the waveform because many data distortions and errors (for example, frame loss, header corruption, etc.) are often only detected as a loss of sync, which does not accurately characterize the nature of the data distortions detected.
Further, conventional testing systems typically involve specialized transmitters or receivers, which are not be feasible for cost and/or scalability reasons. For example, bit error rate testers typically need a specialized circuit-based system where specialized testing messages are sent from the transmitting bit error rate tester to a receiving device and then looped back to the bit error rate tester. Often, bit error rate testers measure errors on a continuous basis, which may result in incorrect measurements when transmission frames are discarded or lost. Bit error rate testers also measure average bit error rates and do not provide data required to measure a time-varying characteristics of a communication.
Another example of a conventional system includes forward error correction, which corrects data distortions as the transmission frames are received. In one aspect, forward error correction is used in conjunction with interleavers configured to spread data fields within a layer one frame over time to overcome short time-scale distortions or losses. While forward error correction and/or interleavers ensure low error rates, forward error correction and/or interleavers do not provide detailed analysis of the channel of communication because errors are typically automatically corrected in transit by the interleaving decoders as the transmission frames are being decoded and, therefore, errors are not detected and analyzed.
Generally, packet testers are also used to test communication channels and measure end-to-end performance of packet-based communications. Packet testers typically work at the Ethernet or IP layer of the stack. Test packets in packet tester systems are typically encoded and interleaved in the transmitter, then deinterleaved and decoded in the receiver, resulting in the error rate typically being either zero or one, again losing information about what is happening on the channel. The interleaving and deinterleaving process of the packet tester systems results in a decrease in the number of dropped packets relative to the actual raw error rate (e.g. the time-varying characteristics) of a channel of communication, limiting its effectiveness as a means for measuring raw time-varying channel characteristics.
Adaptive coding and modulation is another conventional system that provides for transmitting modems to adapt the waveform parameters to current channel conditions, but does not provide detailed information about the channel, as the timescales over which adaptive coding and modulation operate are far too long for this purpose. Further, adaptive coding and modulation often does not look at the entire data frame in adapting the waveform parameters, using only a portion of the frame data. This means that adaptive coding and modulation may be analyzing too small a sample in time to capture important effects of misrouting or dropping of frames. Adaptive coding and modulation may also use single frequency measurement tones (also known as pilot tones) going back and forth through the system. However, this also presents very limited insight into the characteristics of the channel of communication as these single frequency measurement tones do not account for the entire channel, only a certain frequency at a certain time.
There is a need for a system that can measure the time-varying characteristics of an entire channel and the distortions that are generated during transmission. It is further desirable if such a system can be attached or adapted to existing hardware, as opposed to requiring specialty hardware.