Microwave Journal

DUEL Base Station IP to Improve LTE Uplink Experience

December 3, 2009

Cambridge Consultants has launched Dual-domain Uplink Equalizer for LTE (DUEL), a breakthrough technology that significantly improves LTE uplink performance when compared to MMSE, the “text-book” receiver design. DUEL, designed as an algorithmic and DSP extension to LTE base station receiver designs, requires no changes to handsets.

LTE technology (Long Term Evolution) is the first step to 4G networks and represents the future direction for cellular network evolution. The LTE uplink (SC-FDMA, arguably where LTE is most novel) supports the transfer of information from users’ terminals to the network. With the rapid growth on the internet of user-generated content fueled by social networks and the prevalence of digital still and video cameras, the uplink will continue to take on a more significant role in influencing users’ perceptions of service quality. Good uplink performance is also critical to good overall internet experience.

LTE promises to deliver high data transfer rates, but these can only be achieved under perfect channel conditions, such as low user mobility (walking speed or lower) and high diversity (low correlation) between receive paths at the base station. There are many occasions when these conditions do not arise, but the users’ expectations will not diminish when this happens. Users will simply become disappointed if the performance they receive drops off. Areas of lower performance appear to users as black-spots or holes and filling these holes in the network increases the cost for the operators.

Cambridge Consultants’ patent pending DUEL receiver improves the performance of the uplink in all channel conditions, filling many of the holes that would otherwise remain. Its unique and highly complex algorithms take advantage of properties of the LTE uplink signal to reconstruct what was transmitted with higher fidelity than a conventional text-book receiver. As a result, it works well even when the signals received by each BS antenna are highly correlated.

Monty Barlow, Group Leader for Digital Signal Processing at Cambridge Consultants, explained: “There were two key challenges that we faced in designing a better receiver. Firstly, we needed to understand the information within the uplink signal that could be used to reconstruct what we received more accurately, which in itself was a mammoth mathematical challenge. Secondly, we needed to find a way to reduce the processing complexity so that it could be implemented within sensible resources. The outcome is that DUEL can be deployed on any base station baseband platform, including DSP, FPGA and even ASIC. Its footprint varies with silicon technology and supported RF bandwidth, but is well within the capabilities of modern signal processing devices. It can also be extended to provide gains on MIMO uplink to support the future revisions of LTE.”

Tim Fowler, Commercial Director in Cambridge Consultants’ Wireless Division, added: “Downlink speeds have traditionally received more focus as consumers look to download multimedia content onto mobile devices. However, with the increase in popularity of mobile micro-blogging, social networking and video-sharing, uplink performance will become more and more important. We believe that this development fills a critical gap in the technology and will benefit both operators and end users.”

Cambridge Consultants has not only designed and modeled DUEL, but has also developed a comprehensive test platform that includes a conventional MMSE-based receiver alongside the DUEL receiver to allow their performance to be compared on the same received signal. This test platform uses a combination of devices from picoChip and Cambridge Consultants’ proprietary VIPER development platform, and includes a real-time uplink transmitter and channel model which can be dynamically varied to explore the performance benefits. The complete test and visualization environment that this platform provides helps to understand the complexities and characteristics of the channel and the performance benefits that are delivered.