MegaMIMO: Independent Wireless Transmission that Scales Linearly with Number of Transmitters


MegaMIMO is the first working system that can scale wireless LAN throughput linearly with the number of transmitters and can be applied to achieve fully scalable wireless networks. 

Problem Addressed

Wireless networks today are limited by interference that occurs when two nearby devices transmit simultaneously, preventing either device from delivering its packet. Recent wireless systems like SAM, IAC and beamforming allow concurrent transmissions across different transmitters in the same interference region and have advanced the state of the art in practical wireless design, allowing wireless networks to double or triple their throughput. Nonetheless, these systems remain limited by the maximum number of antennas on an individual node, and cannot continuously scale the throughput as more transmitters join the systems. The Inventors have developed MegaMIMO, a practical system that overcomes this barrier and enables wireless throughput to increase linearly with the number of transmitters to enable fully scalable wireless networks.


The core component of MegaMIMo is a lightweight distributed phase alignment algorithm that allows N single-antenna access points (APs) to behave as if they were a single giant MIMO AP with N packets concurrently to N clients. The algorithm works as follows: one of the APs acts as the lead, and all other APs adjust their transmitted signals to emulate a scenario where they share the same oscillator as the lead AP. Every joint transmission (i.e. a transmission of concurrent streams) starts by the lead AP transmitting a short synchronization header. The other APs listen to the synchronization header, and use it to discover the difference between their own oscillator phase and the oscillator phase of the lead AP. They can then align the phase of their own transmission with the lead AP by multiplying by the appropriate angle.


This synchronization cannot persist over time because different APs have different frequency offsets, which causes their signals to rotate at different speeds over time. To address this issue, the APs also use the synchronization header to estimate the frequency offset, predict changes in phase caused by this offset, and compensate for them during phase synchronization. MegaMIMO inserts resynchronization symbols periodically in a packet to allow APs to track the phase difference with the lead AP. Since the frequency of resynchronization symbols only depends on measurement error, and does not change with the increased number of APs, the overhead of such symbols is a small constant that becomes negligible as the number of APs increases. 


  • MegaMIMO can deliver a median throughput gain of 9.4x in a 10 AP network