Overview

The modem modulation method called INTRA (INformation TRAnsformations) is based on Wavelet Theory. With INTRA, the data-rate for networks can be increased by a factor of 2 to 4 over the current state-of-the-art for LANs and MANs based on simulations. INTRA modems can achieve this remarkable performance at very low cost.

Figure 1 illustrates the concept. The INTRA transmitter is a look-up table driving a low cost CMOS D/A converter directly at RF frequency even though there is no carrier. The receiver for one channel is shown as a Surface Acoustic Wave Filter (SAW) followed by one comparator. There is no A/D converter or DSP in this INTRA receiver. Many other configurations with and without SAWs, IF mixers, and multiple bits-per-symbol are possible for both CATV and LAN applications.

The operation of an INTRA modem can be explained in several mathematically equivalent ways. From a Wavelet perspective, the transmitter sends a short burst of narrow-band RF energy ---called a wavelet--- for each data symbol. It can be called "RF" (or IF) energy since D/A converters are inexpensive, so the output can cover any narrow sub-band from DC to about 100 MHz even though INTRA is fundamentally a baseband modem with no carrier frequency.

Each wavelet extends over several symbol periods. If the wavelets are orthogonal they are uncorrelated so there is no interference from other wavelets. Thus there is no Inter-Symbol Interference (ISI) and no Adjacent-Channel Interference (ACI). Wavelets can be generated and received by matched transversal (FIR) digital filters. Simulations show this all-digital design has no spurious response.

In the illustration, the receiver uses an analog SAW filter and comparator to correlate the received waveform with the known wavelet shape. Here the sign of the correlation determines if a 1 or a 0 was received. The correlator will suppress ingress noise or RFI (RF Interference), since RFI does not resemble the wavelet's waveshape (i.e. uncorrelated). This is akin to the suppression of jammers in a military spread-spectrum correlation receiver.

The small number of possible binary inputs and wavelet outputs allows the transmitter filter to be implemented as a ROM look-up table (or gate array). A RAM look-up could be used instead with the coefficients of the equivalent FIR filter adapted to pre-equalize the wavelet for any distortions in the cable. INTRA modulation is equivalent to an FIR vector-filter and is therefore its own equalizer (a separate equalizer is unneeded).

The design in Figure 1 can be extended to send LAN data over twisted pair by taking into account the strong frequency dependence of the S/N ratio. For twisted-pair the signal power, S, experiences a frequency-dependent loss. And on twisted-pair bundles, the primary source of noise power, N, is cross-talk, which is also frequency dependent..

For wireless applications, bandwidth efficiency, non-coherent reception and constant envelope modulation are often desirable and a novel FM modem that offers these benefits is patent pending. Another feature of the carrierless baseband modulation in Figure 1 is that it can switch to any band at an IF frequency. The switching is extremely fast and without unwanted spurious noise, so that a frequency-hopped wireless LAN can have fast hop rates (i.e. faster than the symbol rate) because there is no phase-locked loop in the system.

Another patent application has been submitted for an unprecedented new class of bandwidth efficient networks suitable for digital voice and that does not use digital compression algorithms. This new concept for commercial voice and video networks is a continuation of the digital encryption and spread spectrum principles described in US Patent No. 5,367,516. For battlefield networks INTRA is superior to the state-of-the-art for its LPI.

Background Concepts

Modulation and demodulation are mappings that can be denoted by the operators [M] and [D]. To recover the data correctly, [D][M] = [I] = IDENTITY for any modem. (Note that operators work from right to left, and an overall delay is still considered IDENTITY). If [M][D] = [D][M] over the bandwidth of the channel, then the operators are said to commute and the operators are therefore "rotations" (explained below).

For a perfect Commuting Operator Modem (COM), a bandlimited Gaussian analog input signal, g, can be demodulated and re-modulated at the transmitter since [M][D]g = g. Thus a COM can send the maximum possible entropy, so it is an optimal transmitter. Since the operators can pass a Gaussian, they can be used to digitally encrypt any analog signal. For example, the baseband portion of, say, an INTRA Cellular Personal Communications transmitter would compute [M][e][D] and the receiver would compute [M][d][D], where an arbitrary digital encryption [e] and decryption [d] obey [d][e]=[I]. The baseband signal would modulate the cellular system carrier; however, the combined transmitter and receiver can result in an identity [I] if, and only if, [M] and [D] are commuting operators. A change in COM dimensionality allows forward error correction (FEC) and multiple access protocols to be included, so this is really a new form of bandwidth efficient networking without digital compression algorithms.

The commuting operators for INTRA can be constructed as digital matrix operators, since any bandlimited signal can be described by digital samples via the Sampling Theorem. Commuting matrix operators can be interpreted as geometric rotations of a vector in some coordinate system. Therefore, "Information" can be thought of as a vector which can be projected onto DATA or SIGNAL coordinate representations (i.e. axes) by a "rotation" of the axes. The SIGNAL coordinates are the D/A samples. A Commuting Operator Modem performs an INformation TRAnsformation in this way, hence the name INTRA. Mathematically, (i) the Wavelet Transformation, (ii) the matrix operator approach just described, and (iii) certain multi-rate baseband filters are all identical insofar as performing "rotation", so there are several equivalent ways to implement INTRA systems.

The correlation process-gain of INTRA provides an inherent immunity to interference that is comparable to the jamming rejection of a conventional spread spectrum system, except that INTRA does not spread the spectrum. Conventional spread-spectrum wastes bandwidth in order to obtain this immunity to interference. INTRA does not expand the bandwidth with a spreading function --- in fact, INTRA spectra can overlap due to the properties of wavelets so it is more bandwidth efficient than any other modulation. INTRA's immunity to interference comes by spreading symbols in time rather than frequency, and since the time waveforms of wavelets can also overlap there is no penalty in data-rate.

INTRA theory even predicts that analog NTSB can be digitally encrypted, say with the DES algorithm, and then returned to analog without expanding the analog bandwidth ---this is a breakthrough giving absolute protection unattainable in analog TV scramblers. And upstream analog voice and video can be sent digitally without using compression algorithms, so low-cost in-home cameras can be plugged directly into inexpensive INTRA modems.

In summary, INTRA is a baseband (carrierless) modulation using multidimensional invertible transformations. This allows new block diagrams for modems (i.e., with and without A/D converters), and provides new possibilities for transmitting information in all forms (analog or digital input on wireline RF, optical, sonic, magnetic storage media etc.).