Next Generation Copper Bonding Technology: MIMO-on-DMT (ADSL2 & VDSL2)
Aktino leverages a combination of both MIMO (Multi-Input-Multi-Output) techniques and Discrete Multi-tone (DMT) as the foundation for its copper bonding technology because it provides unparalleled performance compared to legacy HDSL and E.SHDSL copper bonding technologies. MIMO techniques for wireline applications were first introduced by Aktino in 2003 with support from service providers and silicon vendors. Aktino’s MIMO-on-DMT solutions are now in their 4th year of deployments with many North American ILECs and are in trials with several European service providers. These providers have not only validated the superior performance claims over E.SHDSL technology or non MIMO-on-DMT based technologies like bonded ADSL2, but they’ve all seen the significant benefits first-hand of using MIMO in key applications like mobile and DSLAM backhaul and business services applications.
MIMO Mitigates Interference
It has long been understood that crosstalk is the limiting factor for all DSL transmission. Ultimately, it is crosstalk that determines the true rate and reach of any DSL line today. However, until the Aktino solution was introduced, there has been no practical method of removing or canceling crosstalk. Fortunately, this is where MIMO techniques can and have had a major impact.
By treating the groups of bundled copper pairs (called “binder groups”, typically consisting of 25 to 100 pairs per group) as a multiple-input/multiple-output channel and creating a transceiver which treats multiple pairs together, it is possible to separate crosstalk from signal. The MIMO transceiver performs joint signal processing across all the pairs it controls and creates a mathematical picture of the crosstalk environment those pairs inhabit. The mathematical picture is constantly recalculated and updated to ensure that the best possible decision is made using this information. When the MIMO techniques are used the results can be startling. Transmission rates can be increased by factors of 2X compared to today’s best DMT modem or 10X compared to echo canceled legacy modems (HDSL, SHDSL). These are the kind of increases in performance that drive substantial economic benefits for providers and have defined the next generation of copper bonding technology.
DMT is a Proven Technology, Provides Superior Spectral Compatibility and Supports Both Symmetric and Asymmetric Bandwidth
MIMO processing can theoretically be applied to any line code used in wireline transmission. However, there are very good reasons why Aktino selected Discrete Multi-tone (DMT) as the foundation for its copper bonding technology. First, even without MIMO processing, DMT is a superior line code that is one of the most widely used line codes in the wireline world as both ADSL2 and VDSL2 are DMT-based. Thus, it's been at the forefront of significant and ongoing technology advances and cost reductions. In leveraging DMT, Aktino and it's customers alike benefit from this.
Second, there are many kinds of impairments in wireline transmission including attenuation of the line, imperfections in the line such as bridge taps and splices, radiated interference such as Ham radio transmissions and broadcast radio, TV, etc. However, one of the key attributes of DMT is its ability to work around narrow-band interference. For example, when interference exists that tends to make a portion of the frequency spectrum unusable, with a DMT system it's still possible to have complete and unimpaired use of the entire remaining portion of the frequency spectrum. With single carrier systems such as HDSL, SHDSL and QAM the entire system performance is degraded and sometimes made unusable by a single narrow-band interferer.
Third, DMT systems provide superior spectral compatibility with ADSL and VDSL they are also DMT-based and DMT systems are immune to DMT generated cross-talk. When DMT is used in longer reach applications (greater than 5 Kft/1.5 Km of twisted copper pairs) and used in a frequency division multiplexed format (FDM band separation is the most widely deployed method for full duplex operation in DMT systems), there is essentially no cross talk interference caused by similar DMT transceivers on neighboring transceivers. This eliminates the complexity and cost of echo-cancelation processing that other line codes like E.SHDSL use. For example, under heavy alien disturber scenarios, bonded ADSL2 can lose up to 50% of downstream and upstream bandwidth. Aktino’s MIMO can recover most of these losses.
Finally, DMT enables Aktino to provide programmable symmetric and asymmetric services, which ensure efficient bandwidth use in several different applications like backhaul, but also make it possible for providers to offer new broadband services that they can’t offer using other bonded copper solutions.
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