Coherence Diversity in Frequency and Time

Description:

The University of Texas at Dallas is seeking companies interested in commercializing a diversity scheme for wireless networks, called coherence diversity, which provides a novel source of gain that is distinct from other kinds of diversity. As individual links in a wireless network often experience unequal fading coherence times and coherence bandwidths due to differences in mobility or scattering environment, the described scheme uses such disparities to improve system performance. Using a coherence diversity scheme improves the achievable rates for broadcast channels in several cases. Achievable rates are attained using a generalization of the method of product superposition to determine the best opportunities to re-use certain slots without contaminating the pilot resource for users requiring it. The central idea of this achievable rate involves transmitting a pilot whenever one or more receivers experience a fading transition and allowing exactly one other receiver (who does not need the pilot) to simultaneously utilize the channel for data transmission. Coherence diversity schemes provide a novel source of gain that may be used to improve the achievable rates for broadcast channels in a variety of fading conditions.

Technical Summary:

In all combinations where two channels have non-identical dynamical characteristics, coherence diversity may be applied to achieve gains. This is made possible by product superposition, a method that allows the signal of one less-selective user to “disappear” into the equivalent channel seen by the other more-selective user. This allows the re-use of some pilot resources (time/frequency) to send data to the users that do not need that pilot resource, without contaminating those same pilots for the users that indeed need them. Unlike multiuser diversity, which only provides power gain, coherence diversity improves the degrees of freedom. Furthermore, coherence diversity does not require multiple antennas, unlike spatial diversity. Coherence diversity can be used to enhance the throughput for existing systems and has the potential to be implemented into massive multi-input multi-output (MIMO) systems and 5G telecommunications standards.

Value Proposition:

The coherence diversity scheme takes advantage of the unequal fading conditions for users in a variety of wireless channels in order to optimize gains in the system achievable rates.

Applications:

Wireless networks – Broadcast, multiple access, and MIMO channels
Cellular systems – Current (4G/IMT-Advanced) standards and potential 5G mobile networks
Internet of Things – Improved throughput for connected devices that experience unequal fading conditions

Key Benefits:

Novel Gains – Achieved from unequal fading conditions, such as disparate mobility and/or scattering environments, between users
Enhanced Throughput – Obtains “free” rate to the users with less selectivity in time or frequency
Operating range – Improves the achievable rates for broadcast and multiple access channels in a variety of environments

Inventors:

Aria Nosratinia, Ph.D.

Mohamed Shady

Publication:

Fadel and A. Nosratinia, Coherence Disparity in Broadcast and Multiple Access Channels, IEEE Transactions on Information Theory vol. 62, no. 12, December 2016, pp. 7383-7400.

Fadel and A. Nosratinia, "Coherence Diversity in Time and Frequency," 2016 IEEE Global Communications Conference (GLOBECOM), Washington, DC, 2016, pp. 1-6.