| NSF Org: |
CCF Division of Computing and Communication Foundations |
| Recipient: |
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| Initial Amendment Date: | January 18, 2013 |
| Latest Amendment Date: | June 11, 2015 |
| Award Number: | 1256548 |
| Award Instrument: | Standard Grant |
| Program Manager: |
John Cozzens
CCF Division of Computing and Communication Foundations CSE Directorate for Computer and Information Science and Engineering |
| Start Date: | February 1, 2013 |
| End Date: | January 31, 2015 (Estimated) |
| Total Intended Award Amount: | $265,207.00 |
| Total Awarded Amount to Date: | $265,207.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
450 JANE STANFORD WAY STANFORD CA US 94305-2004 (650)723-2300 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
350 Serra Mall Stanford CA US 94305-4027 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | SIGNAL PROCESSING |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.070 |
ABSTRACT
This research studies the use of power combining in multi-antenna radios. Modern radio systems often use multiple transmit antennas and appropriate signal coding to improve throughput and reliability of wireless links. Ideally, each amplifier should be rated at the maximum total (or sum) power that can be transmitted from all antennas. Due to cost and efficiency considerations, the power rating is usually designed to be lower (typically the maximum total power divided by the number of antennas), and this can lead to significant performance loss. This research explores a solution using Power Combining Networks (PCN) that enable the output of an amplifier to be switched/combined into any antenna, thus moving power from a weaker to a stronger antenna, resulting in improved link performance.
The maximum output power of a MIMO (Multiple Input, Multiple Output) antenna transmitter is limited due to bio-safety considerations. MIMO transmission performs best when each power amplifier is rated at the full system transmit power. If the amplifiers are fractionally rated due to cost and efficiency considerations, the worst case loss with M antennas can reach log M dB in the presence of channel imbalances. A PCN can reduce this loss significantly, trading the loss of array gain for a better channel coupling efficiency. Use of a PCN alters the effective MIMO channel and therefore can also change the optimum transmit coding. The goal of this research is to study fast algorithms for PCN selection, appropriate signal coding schemes and the best realizable performance.
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Modern wireless systems (Cellular, WiFi) incorporate a key technology known as MIMO (Multiple Input, Multiple Output). MIMO improves throughput and reliability of wireless links. MIMO requires the use of multiple antennas at the transmitter (and receiver) and involves sending different waveforms from each of the transmit antennas. Typically each transmit antenna has its own associated Power Amplifier (PA). Ideally, each PA should be rated at the maximum total power that can be safely transmitted from all antennas. However, due to cost and efficiency considerations, the PA power rating is usually designed to be at maximum allowed total power divided by the number of antennas. This design economy has a side effect. If the channel (link gain) from a particular transmit antenna to the receiver antenna(s) is weak, a phenomena caused by multipath induced fading, the power fed to that transmit antenna is wasted. A solution to this problem is a Power Combining Networks (PCN) that allows output of any PA to be switched/combined into any of the transmit antennas, thus moving power, if necessary, from a weaker to a stronger antenna. This can result in improved link performance. PCNs have been used in practical MIMO systems.
The project was aimed at further improving PCN technology. The main project outcomes were as follows.
The problem of deciding which PA should be switched and combined to which antenna can be numerically intensive. We developed fast (numerically efficient) algorithms for this problem
In some MIMO schemes, a technique known as beamforming is used, causing directional focusing of radio energy. Such focusing can create bio-hazard in devices held close to the human body. The PCN problem has to be reformulated with beamforming and we developed some simple, but sub-optimal, approaches.
The normal PCN operation assumed perfect knowledge of the instantaneous MIMO channel. In certain high mobility situations, this may be hard to obtain and we may only have the statistical knowledge of the MIMO channel. We developed PCN algorithms when only statistical knowledge was available.
Wireless transmission are inherently broadcast (i.e., receivers other than the intended one also may receive (overhear) the transmission). In multi-hop networks, this overheard information can be used at a later time to improve overall performance. Use of PCN in such cases needs a new formulation and we developed some solutions
In summary this project developed a number of new algorithms to improve and expand the use of PCN technology to enhance the performance of wireless systems
Last Modified: 05/08/2015
Modified by: Andrea J Goldsmith
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