This invention provides a new method of simultaneously addressing two major problems in high-capacity wireless communications: signal fading and interference. The...
This invention provides a new method of simultaneously addressing two major problems in high-capacity wireless communications: signal fading and interference. The technology consists of a new signal control algorithm that reformulates the minimum mean squared error (MMSE) criterion. Adaptive receivers for interference suppression based on the standard MMSE criterion fail over fading channels. In contrast, adaptive interference suppression based on the new differential MMSE (DMMSE) criterion is robust over rapidly varying fading channels and provides large performance and capacity gains over conventional receivers for code division multiple access (CDMA) systems. The DMMSE criterion also provides beamforming and equalization receiver techniques for CDMA systems, which converge rapidly without requiring any training overhead. These receiver innovations are directly applicable to second- and third-generation CDMA commercial cellular networks as well as to spread spectrum and CDMA-based military communication systems.
This technology uses an adapted minimum mean squared error criterion to successfully solve the problems of signal fading and interference without using up bandwidth. It also enables successful equalization and beamforming for receiver antenna arrays for code division multiple access systems.
How It Works
This invention reformulates the MMSE criterion so that it applies to systems in which the data being tracked are the ratios of the data appearing in successive observation intervals. The new differential MMSE criterion leads to a number of novel algorithms for adaptive implementation of the MMSE receiver. The result is that signal fading and interference are prevented without using the bandwidth that other systems require. A standard linear MMSE receiver minimizes the mean squared error between the receiver output and the desired sequence. Such a receiver uses adaptive algorithms that are initialized by a known training sequence. However, if the desired sequence varies rapidly over time, the adaptive algorithms are unable to compensate for the unknown gain. Thus, while MMSE interference suppression is well known to give better performance and increased capacity for CDMA systems than conventional reception, these benefits have been difficult to realize in practice.
This invention uses a new differential MMSE criterion that assumes that the unknown gain is roughly constant over two observation intervals. Using the criterion, the desired data can be tracked without the need for explicitly estimating or tracking the unknown gain. This makes adaptive interference suppression practical for commercial CDMA systems, thus providing significant gains (in terms of either the number of users supported or the bandwidth per consumer) over conventional receiver techniques. This invention also addresses the shortcomings of existing methods used in beamforming applications for receiver antenna arrays. For direct sequence CDMA systems with long spreading sequences, current methods require that training symbols be included in the transmission. However, a novel application of the DMMSE criterion removes the need for training altogether, using instead the receiver's knowledge of the spreading sequence.
The resulting beamforming and equalization algorithms perform all the benefits of training-based algorithms without any of the overhead. Use of the DMMSE criterion in receiver design optimizes the use of scarce wireless bandwidth by allowing more users to be supported for the same bandwidth or providing a larger bandwidth per user. The new techniques are directly applicable to second- and third-generation cellular and personal communication systems as well as to direct sequence spread spectrum-based military communication systems. Implementing this technology may require minor changes in hardware configurations; however, these changes would be simple and inexpensive. And the resulting increase in available bandwidth will make the benefit well worth the cost.
Cellular phones and base stations Personal communication systems Any direct sequence CDMA system with long spreading sequences, including second- and third-generation cellular networks and military communication Other applications where receivers must cope with rapid channel time variations
Conventional receivers in CDMA systems are interference-limited, and vulnerable to the near-far problem. However, advanced interference suppressing techniques are difficult to implement over time-varying channels. The DMMSE criterion enables adaptive receivers that suppress interference while being robust to wireless channel time variations. Increases the capacity and the bandwidth per user in wireless networks Suppresses interference while being robust to fading for CDMA systems with short spreading sequences Provides superior beamforming and equalization, without requiring any training, for CDMA systems with long spreading sequences
A novel technique for data transmission that uses vibration motors in all cell phones as transmitters and accelerometers as receivers. By carefully regulating the...
A novel technique for data transmission that uses vibration motors in all cell phones as transmitters and accelerometers as receivers. By carefully regulating the vibrations at the transmitter and sensing them through vibration sensors, two mobile devices can communicate.
This is useful for security-sensitive applications such as mobile payments because vibrations are inherently more secure than RF broadcast in NFC or Bluetooth. The ubiquity of vibration motors in every cell phone, even in developing regions, presents an immediate market for vibratory communication